Prince William and Prince Harry head to Balmoral every summer to spend time with Queen Elizabeth II and the other members of the royal family. Even though the royal siblings have a blast with their family there, they also remember the vacation destination due to a heartbreaking reason.

When Prince William and Prince Harry were just 15 and 12 years old, respectively, they were vacationing in Balmoral with Prince Charles and Her Majesty. While enjoying their time there, the royal siblings also had the opportunity to talk to Princess Diana on the phone.

At that time, Princess Diana was in Paris with her boyfriend, Dodi Al Fayed. But what Prince William and Prince Harry didn’t know was that phone call would be the last time that they will ever get to talk to the Princess of Wales.

Prince William and Prince Harry were still in Balmoral when they found out that their mom was killed in a fatal car crash. They were supposed to see Princess Diana the next day after her trip to Paris, but they never got the chance to reunite with her.

In the book “William And Catherine,” details of Prince William’s last conversation with the late royal were revealed. Royal author Andrew Morton said that the dad of three was actually feeling worried about his younger brother at that time.

“While Diana lay on the deck of a luxury yacht under the Mediterranean sun, William was concerned about an edict from Buckingham Palace that he had to attend a photocall to mark his third year at Eton,” Morton said. “It was part of what he considered a Faustian bargain made with the media — he would be left alone to continue his schooling in peace in return for occasional access,” he added.

The problem, according to Morton, had to do with the fact that Prince Harry repeated an entire year during his pre-school days in Ludgrove. And as such, the focus of the press would’ve been on the Duke of Sussex’s lack of achievement and not on the future king’s academic progress. Even at a young age, Prince William was already protective of Prince Harry.

Princess Diana, Prince Harry and Prince William Princess Diana (L), Prince Harry, (C) and Prince William (R) gather for the commemorations of VJ Day, 19 August 1995, in London. JOHNNY EGGITT/AFP/Getty Images