Rooney Mara stuns in lacy black frock as she supports her fiance Joaquin Phoenix at The Joker premiere at the Toronto International Film Festival

• e-mail

It wasn't an easy role to play. Joaquin Phoenix admitted to 'going mad' after he lost 52lbs to play the Joker in the upcoming thriller. 

But Phoenix, 44, had a support system right behind him that includes his fiancée, Rooney Mara, who attended the premiere for The Joker alongside her beau on day five of the Toronto International Film Festival at Roy Thomson Hall on Monday.

Mara, 34, stunned in a lacy black frock for the red carpet event.

Support system: Rooney Mara, 34, attended the premiere for The Joker alongside her beau on day five of the Toronto International Film Festival at Roy Thomson Hall on Monday

The dress featured a strapless, sweetheart neckline with bunched fabric on the sides.

The Girl with the Dragon Tattoo actress donned a pair of pointy black heels on her feet, while her hair was braided across her crown and swept up into a bun.

She accessorized with a few silver rings, allowing her dress to do most of the talking.

Mara's makeup featured rosy, warm eyeshadow and a pink pout.

Bun head: The actresses hair was braided across her crown and swept up into a bun

Rosy glow: Mara's makeup featured rosy, warm eyeshadow and a pink pout

Frock: Mara's dress featured a strapless, sweetheart neckline with bunched fabric on the sides

Monochrome: The Mary Magdalene star  stunned in a lacy black frock for the red carpet event

Keeping it simple: Rooney accessorized with a few silver rings, allowing her dress to do most of the talking

Phoenix rocked a dapper black tux with a black tie.

He paired the red carpet look with a pair of black dress shoes and a white dress shirt.

The Walk the Line star's salt-and-pepper locks were slicked back over his ears as he posed for photos. 

He'll be the seventh actor to take on the role of the Clown Prince Of Crime, also known as Arthur Fleck. 

Dapper: Joaquin Phoenix rocked a classic black tux with a black tie

Black and white: Joaquin paired the red carpet look with a pair of black dress shoes and a white dress shirt

Deemed the most 'deranged' Joker yet: Joaquin will be the seventh actor to take on the role of the Clown Prince Of Crime

'Why so serious?': The actor couldn't help but put a smile on his face as he arrived at the event, mirroring his iconic character, as he met with an adoring mob of fans

Beaming: He smiled ear to ear on the red carpet

Cast and drew: Joaquin was joined on the red carpet by his co-stars Zazie Beetz, Robert De Niro, and Frances Conroy as well as Director Todd Phillips

Swap! Bradley Cooper, 44, stole Director Phillips spot for a photo with his co-stars

The actor couldn't help but put a smile on his face as he arrived at the event, mirroring his iconic character, as he met with an adoring mob of fans. 

Joaquin was joined on the red carpet by his co-stars Zazie Beetz, Robert De Niro, and Frances Conroy as well as Producer Bradley Cooper and Director Todd Phillips.

Beetz, 28, looked fierce in a black wrap dress and thigh-high boots.

She wore her long raven locks in braids that fell all the way down to her hips. 

Work it! Zazie Beetz, 28, looked fierce in a black wrap dress and thigh-high boots

Locks of love: Zazie wore her long raven locks in braids that fell all the way down to her hips

Robert De Niro, 76, wore his white hair combed  back. 

The Meet the Fockers star wore a blue suit with a grey collared shirt underneath.

He paired the look with black dress shoes as he smiled and joked with his co-stars on the red carpet.

The actor plays Murray Franklin in the drama, a talk show host who plays an 'instrumental' role in Arthur's downfall according to the Hollywood Reporter.

Mature: Robert De Niro, 76, wore his long white hair combed back; pictured with Zazie Beetz

Having fun: De Niro posed with his co-stars

Black and blue: The Meet the Fockers star wore a blue suit with black dress shoes

A-listers: Robert paired the look with a grey collared shirt as he smiled and joked with his co-stars on the red carpet

Bradley Cooper, 44, also wore a black suit for the black tie event. 

The A Star is Born actor paired the look with an appropriate black tie, black dress shoes and a blue dress shirt.

Cooper is a producer on the film along with director Todd Phillips via their production company, Joint Effort.

Twins: Bradley Cooper, 44, also wore a black dress shoes for the black tie event

The A Star is Born actor paired the look with an appropriate black tie

Black on black: The actor matching Phoenix in a black suit

Black and blue: Bradley paired the look with a blue dress shirt

Happy hugs: The cast shared lots of hugs and laughter as they walked the red carpet

Todd Phillips looked dapper in a grey suit and  brown tie.

The 48-year old director wore a white and brown patterned business shirt under his suit and brown dress shoes on his feet.

Well-to-do: Todd Phillips, 48, donned a grey suit and brown tie

Patterned: The director wore a white and brown patterned business shirt under his suit and brown dress shoes on his feet

Dream team: Cooper is a producer on the film along with director Todd Phillips via their production company, Joint Effort

Frances Conroy, 65, looked comfortable in a black dress.

The Six Feet Under actress paired the look with a black shawl and black ballerina flats.

She accessorized with a beaded necklace while her hair fell down her shoulders in styled curls. 

Frances Conroy, 65, looked comfortable in a black dress and black ballerina flats

Also in attendance were Edward Norton, 50, and his wife, Shauna Robertson, 44.

Both looked more casual than the cast of Joker, wearing black on top and bottom.

Norton paired black pants with a black jacket and sneakers while Robertson opted for a black short-sleeve blouse with black jeans and black boots. 

Power couple: Also in attendance were Edward Norton, 50, and his wife, Shauna Robertson, 44

Matchy matchy: Norton paired black pants with a black jacket and sneakers while Robertson opted for a black short-sleeve blouse with black jeans and black boots

 While speaking to The Hollywood Reporter about playing the Joker, Phoenix claimed that losing weight in preparation meant that he started  'to go mad.'

'The first thing for us was the weight loss. I think that’s really what I started with. And, as it turns out, that then affects your psychology. You start to go mad when you lose that amount of weight in that amount of time,' he explained. 

And Phoenix isn't the only actor to go full out for the role, as the late Health Ledger went fully method for his wild Oscar-winning turn in Christopher Nolan's 2008 The Dark Knight, as he never broke character while on set.

Ledger's co-star Christian Bale told The Hollywood Reporter that the actor was so into his character that he even demanded he 'hit him for real' during a scene.

Stressful: While speaking to The Hollywood Reporter about playing the Joker, Phoenix claimed that losing weight in preparation meant that he started 'to go mad'

Iconic role: Phoenix is the seventh actor to take on the role of the Clown Prince Of Crime (pictured in a film still) 

'As you see in the movie, Batman starts beating the Joker and realizes that this is not your ordinary foe. Because the more I beat him the more he enjoys it. The more I’m giving him satisfaction...And he’s going, “Go on. Go on. Go on….” He was slamming himself around, and there were tiled walls inside of that set which were cracked and dented from him hurling himself into them. His commitment was total.,' he explained.  

Phoenix follows in the footsteps of Ledger, Mark Hamill, Jack Nicholson, and Jared Leto and many more.

In the standalone film in the DC universe, he depicts Arthur Fleck's descent into madness in 1981 Gotham City, as he struggles to make ends meet while living with his mother and is also affected by a a condition that makes him sputter a pathological laugh even in the most inopportune moments.

Joker will be released in cinemas across the UK and the USA on October 4, 2019. 

Jokers: Phoenix isn't the only actor to go full out for his role, as Health Ledger and Jared Leto also went fully method (L-R)