This tragic picture shows hero PC Keith Palmer posing happily with a tourist minutes before he was stabbed to death in a terror attack on the Houses of Parliament.
The photo was taken by US tourist Staci Martin as she posed with the officer just 45 minutes before he was stabbed to death by terrorist Khalid Masood.
Detectives named Masood on Thursday afternoon, just over 24 hours after he mowed down dozens of pedestrians on Westminster Bridge before fatally stabbing Mr Palmer outside Parliament.
Ms Martin was visiting London from Florida when she asked to take a picture with the brave officer outside the Houses of Parliament on Wednesday.
She told ABC news: "It's my first time in London and I see his hat and I'm like I have to take a picture of him with his hat.
"I walked up to him and said 'do you mind if I take a picture?' He said 'no problem', he was really nice."
Less than an hour later, Ms Martin was in a taxi when she heard there had been a shooting and saw a helicopter and emergency vehicles.
She later recognised PC Palmer from the photo released after it was confirmed he had been killed in the horrific attack.
Ms Martin believes the picture with the officer must be one of the last photos of him taken alive.
She said she feels "obligated" to get it to his family, adding: "I just want to make sure they have that of him."
Two teenagers also shared a moving photograph of the officer taken while he was on duty and stationed in front of Big Ben.
A-level students Will Robins and Tyler Chatterley-Russell, both 16, told the Standard they took the photograph while on a college trip to London last year.
The pair described how it was PC Palmer’s idea for the boys to pull funny faces in the photo, after the officer was initially pictured in the background of the shot.
On Thursday tributes poured in to the husband and father, with the Police Federation saying they have been left “numb” by the killing.
A fundraising campaign set up after his tragic death raising money for Mr Palmer’s family raised over a £300,000 in less than one day.
PC Palmer had served in the Metropolitan Police for 15 years but died at the scene after paramedics fought to save his life.
Tributes for Westminster & Parliament Attack
Moments after Mr Palmer was stabbed, Masood was shot dead by police.
He claimed at least four victims before he was killed.
Two people - American Kurt Cochran and Spaniard Aysha Frade - were also killed and about 40 others hurt on the bridge.
A fourth victim, a 75-year-old man who has not yet been named, was confirmed dead by officers. He died in hospital on Thursday.
Up to 40 other people were also injured in the attack, with casualties including Britons, French children, Romanians, South Koreans, Greeks, and people from Germany, Poland, Ireland, China, Italy and the United States.
Three police officers were also hurt, two of them seriously.
Crowds of Londoners gathered at a vigil in Trafalgar Square on Thursday to pay tribute to those killed and injured in the Parliament attack.
London attack: Trafalgar Square vigil
The Mayor of London, Sadiq Khan, invited both residents and tourists to join a candlelit memorial at the central London landmark in solidarity with victims.
The sombre gathering marked one day since London was targeted in a bloody assault.
Mr Khan had encouraged “everyone visiting our city” to join together in memory of those who lost their lives and “to show the world that we are more committed than ever to the values that we hold dear - that we remain united and open”.
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