It’s been 21 years since Princess Diana passed away, but she is still missed by millions of people all over the world.

While Diana’s fans miss her dearly, nobody misses her more than her beloved sons, Prince William and Prince Harry. Though the two royal brothers rarely speak about their mother’s death, they recently opened up to reveal why they are still haunted by the final phone call they had with her.

Diana was on vacation in France on August 30, 1997 when she called to check on her sons, who were vacationing in Scotland at the same time. William and Harry were 15 and 12 at the time, and like most children, they were eager to get back to playing with their cousins rather than talk to their mother on the phone.

“Harry and I were in a desperate rush to say goodbye, you know, ‘see you later,’” William recalled. They had no idea that their mother would pass away hours later in a car crash just after midnight.

“If I’d known now what was going to happen, I wouldn’t have been so blasé about it,” William added. “But that phone call sticks in my mind quite heavily.”

Harry said that he also has felt guilt and regret about the final call.

“Looking back on it now, it’s incredibly hard. I’ll have to sort of deal with that for the rest of my life,” Harry said. “How differently that conversation could have panned out if I’d had even the slightest inkling her life was going to be taken that night.”

Through their grief, William and Harry have kept Diana’s legacy alive by devoting themselves to many of the charity efforts that she loves. She would certainly be proud of them both and the young men they have become!

William has also made sure that his three children know that Diana was their grandmother, even having them call her “Granny Diana.”

“Just to remind them that there were two grandmothers in their lives,” he said.