Both Prince William and Prince Harry inherited "elements of the serious and the fun" from their grandfather Prince Philip
Prince Philip, Prince William
Prince Philip and Prince William
| Credit: Chris Jackson/WPA Pool/Getty

Prince Philip, who died on April 9 at the age of 99, played a major role in preparing his grandson Prince William to be the monarch one day.

"Philip was crucial in helping coach William as a future King," historian Robert Lacey, author of the bestselling biography Battle of Brothers, tells PEOPLE in this week's cover story. "It was Philip's idea to set up the lunches between William and his grandmother. When the time came for the Queen to talk business with William, Philip would quietly excuse himself because he didn't feel that the constitutional side of the Queen's job was something he wanted to interfere in."

Prince Philip, who insiders say was the glue behind the royal family for more than 70 years, passed on "elements of the serious and the fun" to grandsons Prince William, 38, and Prince Harry, 36, adds royal biographer Penny Junor.

Prince Harry and Prince Phillip
Prince Harry and Prince Philip
| Credit: Phil Walter/Getty

Harry "very much got his sense of duty and active service from his grandfather," says Junor. "Because Harry is a much more relaxed character, he was able to bring in the more frivolous memories of his grandfather" in his tribute statement, including references to barbecue and beer.

prince philip, prince william, prince harry
Prince William, Queen Elizabeth, Prince Harry and Prince Philip
| Credit: Getty

The world was watching as Prince William and Prince Harry reunited at Prince Philip's funeral on Saturday. The two walked in the procession behind their grandfather's coffin separated by their cousin Peter Phillips, but William and Harry chatted together casually as the family exited the chapel following the service.

"The procession choreography, in retrospect, was a mistake," Lacey tells PEOPLE. "As we saw, they could have walked side-by-side quite happily after all. What pleased me afterward was that it all seemed so totally natural, and they drifted to each other like the old days."

Get the premiere issue of PEOPLE Royals for glamorous new photos and inside stories royals fans haven't seen or read elsewhere! Subscribe at

Harry and William were seen chatting alongside William's wife Kate Middleton as they left St. George's Chapel in Windsor Castle. The siblings continued speaking as they walked away from the church, as Kate stepped back to talk with Sophie, Countess of Wessex.

5/3/2021 cover Prince Harry and Prince WIlliam
Prince Harry and Prince WIlliam

Can't get enough of PEOPLE's Royals coverage? Sign up for our free Royals newsletter to get the latest updates on Kate Middleton, Meghan Markle and more! 

Despite tension within the royal family due to Prince Harry and Meghan's step down from royal life followed by their tell-all interview with Oprah Winfrey that aired last month, Prince Philip's death was a time to put family drama aside.

"It has been a very difficult time," a well-connected royal insider says of the past year. "The Duke was the head of the family, and if there were any time they were going to come together, it's now."