So there we were, the future ninth Marquess of Bath and me, on a boat patrolling a lake on his family’s estate, each of us holding a plastic cup full of sprats. All at once, some sea lions surfaced starboard, barking expectantly, their whiskery maws wide open. We hustled to the boat’s railing, emptying our cups, tossing the silvery fish to the appreciative beasts. The marquess-to-be took to this task with particular relish, unsqueamish about getting his fingers slimy and barking back at the sea lions, “Urt! Urt! Urt!” As was only appropriate: he is three and a half years old.

The boy’s mother, Emma, Viscountess Weymouth, was leading me on a tour of the estate, Longleat, which includes a drive-through safari park open to the public. John, my fish-tossing comrade and the elder of Emma’s two sons, was tagging along. The park’s animals include tigers, lions, cheetahs, giraffes, red pandas, gorillas, monkeys, rhinos, hippopotamuses, and an Asian elephant, Anne, who was restored to good health after years of abuse in a circus and now lives at Longleat in her own purpose-built facility with a trio of companion goats. There are also walk-through enclosures where visitors can feed smaller animals, such as tamarins and rainbow lorikeets, and there is the boat ride, where a cup of sprats usually goes for £1, a fee that was waived for his lordship and his adult guest.

The revenues from the safari park and from tours of the Weymouths’ house pay for the upkeep of Longleat, which is situated in the county of Wiltshire, about a hundred miles southwest of London. With 128 rooms, and set on a thousand acres of parkland designed by Capability Brown, the 18th-century landscape architect, Longleat House is one of the best-preserved and most spectacular of England’s stately homes, and has been owned and occupied by the same family since Elizabethan times. (The full estate runs to 10,000 acres and includes an entire village, Horningsham.)

The walls of Longleat House’s rooms and halls are lined with family portraiture—great oil-on-canvas renderings of bewigged men in ruffs and doublets, and pale women with powdered décolletage and hoopskirts. The viscountess’s portrait, by the contemporary artist Paul Benney, stands out for its simplicity. She is wearing the Angelina Colarusso bridal gown in which she was married, in 2013, her straight brown hair grazing her shoulders, striding toward the viewer with a purposeful runway gait. There is another reason the portrait stands out: its subject is the only black person on these walls.

Emma McQuiston was born in 1986 to a Nigerian father and an English mother. When her husband, Ceawlin, Viscount Weymouth, assumes the title held at the moment by his 86-year-old father, Alexander, the current, and seventh, Marquess of Bath, Emma will become Britain’s first black marchioness. In the ranks of British peerage, a marquess and marchioness are second only to a duke and duchess. And someday, young John, a sweet and precociously eloquent boy with caramel skin and loose black curls, will assume his father’s title and become the United Kingdom’s first marquess of color.

The Thynns, to use their family name—Weymouth and Bath are the territorial designations that go with their noble titles; Ceawlin goes by “Ceawlin Thynn” professionally—are, in some respects, a characteristic 21st-century nuclear family: a husband, a wife, and two kids (John has a one-year-old brother, Henry) for whom being mixed-race is unremarkable, secondary to the simple fact that they are a loving unit. But, given their position in the aristocracy, and with Britain poised to celebrate the May 19 wedding of Prince Harry and Meghan Markle, the Thynns are a preview of sorts: here is what a titled British family can look like now—in a way that it couldn’t have as recently as a generation ago.

Emma, an outgoing and strikingly beautiful woman, grants that her significance in this regard is not something that she had planned for. Her racial identity was something that, she insists, went uncontemplated for most of her life. “I was made more ‘aware of myself,’ from the outside in, when I got engaged,” she told me. “I don’t want to not acknowledge the significance, because it has meant a lot to a lot of people. It was a moment in history that people got a lot of hope and encouragement from. But I didn’t do anything on purpose. I just have to appreciate that I’ve been written to personally, and seen it written about, and it’s been taken very seriously.”

This conversation took place in a sitting room in the Thynns’ private apartment at Longleat, a suite of rooms not open to the public. (Emma warned me, as she unlocked a door, that the great-house spell was about to be broken by “a lot of plastic”—the kids’ toys strewn all over the place.) Set out on a coffee table were scones, cupcakes, and meringues that Emma had prepared herself.

Last summer, Emma started hosting afternoon teas for Longleat’s paying public in the Orangery, a 19th-century conservatory, abutting a topiary-intensive garden, where she and Ceawlin exchanged their vows. She is a gifted baker and cook, and is unhurriedly positioning herself to become a homewares and cooking guru—a sort of lower-key, less ascetic, more chill and butter-permissive version of Gwyneth Paltrow in Goop mode. The original basement kitchens of Longleat have been transformed into Emma’s Kitchen, a bright space that sells baked goods based on her recipes and china based on her designs. She plans to hold live cooking demonstrations there, and is in talks with publishers and producers about expanding the Emma’s Kitchen brand to cookbooks and television.

In other words, her ambitions mesh well with those of Ceawlin, an affable, sensible man of vaguely Colin Firth-ian mien who is ever looking to build upon the business potential of Longleat, and who joined us for tea. (His name, which he shares with a sixth-century King of Wessex, is pronounced “SUE-uh-lin.”) Emma has closely read Longleat: From 1566 to the Present, a history published in 1949 by Ceawlin’s paternal grandmother, Daphne Bath, and is keen to revive the atmosphere described in its pages—“hearing the laughter of children,” she said, “and having it be a family home.”

And therein lies an irony of even focusing on Emma’s race. Her union with Ceawlin, far from being disruptive or scandalous, has brought normalcy to a place that has not enjoyed much of it in the past half-century or so.

For decades, “Longleat” has been a byword in the British press for eccentricity, primarily because Lord Bath, the current marquess, Ceawlin’s father, is known for an unusual living arrangement in which he remains married to Ceawlin’s mother, Lady Bath, but keeps an array of mistresses he refers to as “wifelets,” some of whom he has put up in cottages on the property. Lady Bath spends a good part of her time in France. The wifelets have numbered more than 70.

I did not get to meet Lord Bath, but he is a memorable presence in a BBC One documentary series that aired in 2015, entitled All Change at Longleat, which chronicled Ceawlin and Emma’s attempts to modernize the estate while gingerly managing a generational shift in power. Lord Bath ceded control of Longleat’s operations to Ceawlin in 2010, and still lives in his own apartment on an upper floor. In the docu-series, he appears as a plump, messy, libertine character with flowing white hair and a white beard: Gandalf crossed with Galifianakis. The handover, alas, has not proceeded harmoniously. In keeping with the younger generation’s family-friendly mandate, Ceawlin removed some of the lurid, heavily impastoed murals that his father had himself painted on the private apartments’ walls, variously depicting nude figures and Boschian frightscapes. Lord Bath took such umbrage at this action that he boycotted Emma and Ceawlin’s wedding.

Emma, by contrast, enjoyed a more conventional upbringing, even if it was unorthodox at its inception. Her mother, a London social dynamo named Suzanna McQuiston, was a divorced mother of two grown children when she had an affair with Oladipo Jadesimi, a married, Nigerian-born chartered accountant. Emma was the result. Jadesimi returned to Nigeria and went on to prosper as the founder and chairman of the Lagos Deep Offshore Logistics Base (LADOL), which supplies support services to offshore gas- and oil-exploration companies. Today he is among the wealthiest men in West Africa.

Emma was raised in South Kensington, one of London’s poshest enclaves, by her mother and her half-sister, Samantha, who is 21 years her senior. She attended the Queen’s Gate School, a day school for girls (its alumnae include Tilda Swinton and Camilla, Duchess of Cornwall), and thrived socially and academically. She went on to take a degree in art history from University College London, where she became close friends with Ed Tang, the son of the late Hong Kong-based businessman, fashion mogul, and restaurateur Sir David Tang. The younger Tang, who is now an art adviser in New York and the godfather to John, recalls Emma as a self-confident, almost compulsively hospitable force of nature. “Food was a big part of us growing up together,” he told me. “Emma liked to bring me back to her family’s house and feed me: things like Sunday roasts and desserts from scratch, but also Chinese food, a daring thing to attempt around someone with my background. And she passed with flying colors. She was always someone who liked to roll up her sleeves, and always comfortable within herself.”

Among the settings in which Emma found herself at ease as a girl was . . . Longleat. When she was three, her half-brother, Iain McQuiston, the eldest of her mother’s children, married Lady Silvy Thynne, the current marquess’s half-sister. (Lord Bath, ever the iconoclast, dropped the e from his surname in the 1970s.) As a result of this marriage, Ceawlin and Emma became known quantities to each other at family gatherings, though barely: he is 12 years her senior. “So I would be running around,” Emma said, “and he would be sitting down, having a coffee.”

I mentioned to Emma that I had read an interview with her mother in which she said something that, from my American perspective, I found difficult to believe: that Emma had never experienced racism growing up.

“It’s true. It’s really true,” Emma said. “I was just really lucky. I mean, London’s such a cosmopolitan place.” Her mother and sister, she said, “did such a solid job between them of making me feel very settled. My dad’s Nigerian and I grew up in London, and that’s just how it is.”

It wasn’t until 2011, when Emma and Ceawlin, by then 25 and 37, ran into each other at Soho House, the private club in London, that a romance sparked. When they became engaged the following year, they did not anticipate their marriage being any kind of watershed. “From my perspective—and with hindsight I can see that it was incredibly naïve—I absolutely believed that in the U.K. we lived in a post-racial society,” said Ceawlin.

So, I asked Ceawlin, had he no trepidation about going public, no anticipation of racist blowback in aristocratic circles?

“Not for a moment. Not for a moment,” he said. “Not saying there weren’t ripples. You’re probably aware of one in particular.”

Both of Emma’s parents attended her wedding at Longleat. Jadesimi, who goes by the nickname “Ladi,” gave away his daughter while wearing a striped agbada, or wide-sleeved robe, that he’d had made in Nigeria especially for the occasion. However, Ceawlin’s immediate family was represented only by his sister, Lady Lenka Thynn. Lord and Lady Bath opted to attend the wedding of another couple, a pair of polo players, who were getting married the same day.

Lord Bath was still irritated with his son about the murals. Lady Bath was another story. Born Anna Gyarmathy in Hungary and raised in Paris, she married Alexander, the future marquess, in 1969, when she was a model and actress appearing in erotic films under the name Anna Gaël. Ceawlin won’t rehash the matter now, but in September 2015 he told The Sunday Times that he had prohibited his mother from attending the wedding because, in a conversation that they had regarding his engagement to Emma, she said in three different instances that her son’s actions would affect “400 years of bloodline.” That’s when he put his foot down.

“Emma is the least confrontational, least dramatic person, but I don’t think anyone could have that happen at least three times and not just say, ‘Well, fuck this,’ ” he told the Times.

(In the following week’s Sunday Times, Lady Bath gave a rare interview in which she denied that she is racist and said that she would never use the word “bloodline” because “I don’t even know that word. I am not English.”)

In the BBC documentary series, which aired right around the time that Ceawlin’s comments about his mother went public, a bit of a thaw seems to occur between father and son, with Ceawlin and Emma paying a visit to Lord Bath’s apartment with John, then a baby. Lord Bath briefly cradles his grandson in his arms.

In another noteworthy scene, Lord Bath is seen spending time with one of his longest-serving and most age-appropriate wifelets, Sylvana Henriques, who was a Bond girl in 1969’s On Her Majesty’s Secret Service, and who happens to be black. Together, they listen to a song he wrote for her that appeared on a 1974 LP he recorded under the name Alexander Lord Weymouth, I Play the Host. (It was released on Pye Records, the Kinks’ original label.) An acoustic folk ballad, the song includes the lyrics “Hello there, you mulberry-colored venus. . . . We shouldn’t let my whiteness come between us.”

But Ceawlin told me that, for all the TV show’s intimations of rapprochement and mutual understanding, he and Emma are currently in communication with neither his father nor his mother. I asked him if he might make a new push for reconciliation, given that there are now two grandchildren involved.

A pained expression came over his face. “I’d just rather not dwell on it, for the purposes of this article,” he said.

For all the dysfunction within the Thynn family—in interviews, Lord Bath has spoken of a difficult relationship with his own father, the sixth marquess, a slim, elegant, rather more traditionally cheerio-chaps-looking aristo, who died in 1992—Ceawlin acknowledges a maverick streak common to the last three generations of Thynn men, “a thread of not being constrained by other people’s judgments,” as he puts it. His grandfather Henry, for whom his second son is named, was the first British peer ever to open up his home to paying visitors, in 1949.

“It was unheard of,” Ceawlin told me. “I think people within his milieu were quite scandalized.” But Henry’s instincts proved sharp. By 1966, recognizing that Longleat would require significantly greater income still to survive, he opened the world’s first safari park outside of Africa. Today, it receives about a million visitors a year.

Ceawlin and Emma are pursuing an even more audacious path, with plans afoot to break ground in 2019 on a 350-acre American replica of Longleat at a site they have scouted in the eastern United States. There will be a safari park, but their development team’s research indicates that the U.S. customer base, currently in the throes of an Anglophilia fueled by Downton Abbey, The Crown, and, yes, Harry and Meghan, is even more responsive to the concept of walking through a faithfully re-created British manor house. Emma’s afternoon teas have proved a particularly appealing component “for the Englishness I bring,” she said, “the quintessential-homeyness thing that we do here.”

Earlier generations of nobility would have held their noses at such explicit commercial exploitation of their “brands”—and would have asphyxiated themselves in the process. A few years ago, Julian Fellowes, the creator of Downton Abbey, told me that an air of melancholy hangs over the program, set in the teens and 20s, because its aristocratic protagonists, the Crawleys, are “planning for the next hundred years, and they’ll be lucky if they get 20.”

As it happens, Fellowes is friendly with the younger Thynns, and is supportive of their vision. “I think that their modern and imaginative approach to the task in hand is the best thing that could happen to Longleat,” he wrote in an e-mail. “Unlike many of their kind, both of them understand the century they are living in, and one of the central paradoxes of owning a historic house is that the more up-to-date your thinking, the more likely you are to preserve your inheritance and its traditions.”

Here’s another paradox: part of the Thynns’ “up-to-date” appeal lies in their biracial identity. It was a mind-bending exercise to process black Twitter’s exuberant response to the news of Harry and Meghan’s engagement last November. On one hand, the triumphal sense of identification—“Prince Harry’s future mother-in-law is a black woman with dreadlocks. There are no words for this kind of joy,” read one popular tweet—is perfectly understandable. On the other hand, we’re talking about an institution, the British monarchy, that, for most of its existence, has been synonymous with empire and colonization.

I reached out to the Anglo-Nigerian writer Bim Adewunmi, of BuzzFeed, who has written with tenderness and bemusement about her own mother’s love of Princess Diana, to see what, if anything, she made of Emma. Her response was fundamentally “pro-,” if tied up in knots of ambivalence. “So many times, the onus is placed on the racial minority in a space to ‘modernize’ or otherwise fix broken and antiquated structures,” she said. “Emma is one woman, swimming against a vast tide of tradition. And anyway: is she even swimming against it? Maybe she’s just trying to live her best life. But, you know, we see a would-be black marchioness and it means something, even when it doesn’t.”

Emma herself never felt the need to reckon with her “meaning” until she became a public figure. She’s a breezy, effortless conversationalist when talking about food, kids, and Longleat (such as when she points out a Titian, or notes the improbably “sassy” pink sash worn by one of Ceawlin’s male forebears in a portrait), but is more deliberate in assessing her own place in this grand picture.

“When you asked me about the significance of it, the feeling of it, of course, it’s for the children,” she said. “Whatever I’ve done, if it’s to represent something, to move something forward, if that’s how it’s being put, I’m thrilled. But it’s really about our children’s generation. They’re three and one. Can you imagine, when they’re in their 30s, what things will be like?”

At this, Ceawlin looked fondly at his wife—his one and only wife. Henry, the baby, started crying. I dropped half a meringue on the floor. The viscountess picked it up before I could, deflecting my apology. What things will be like? Perhaps, for the first time in ages at Longleat, normal.