The Royal Family are mourning a valued service member.

Graham “Crackers” Craker, who served as a bodyguard to Prince Harry and Prince William at the time of Princess Diana’s death, has died, his sons confirmed. He was 77.

Craker’s sons confirmed his death on social media, according to the BBC, describing him as "an incredible man" who "lived his life so selflessly.”

Craker served as bodyguard to the royal family for 15 years after serving 35 years in the U.K.’s Metropolitan Police before his retirement in 2001. He was also with Harry, then 12, and William, then 15, at Balmoral when they learned of their mother’s 1997 death, with the guard telling The New York Post in 2017 the news was “difficult to take in.”

“From there on,” he added, “it’s the policeman’s instinct to assess the situation and carry on."

Craker walked with the two princes behind Diana’s hearse during her funeral—a memory Harry recounted in his memoir Spare.