In a new BBC One documentary about the life of his grandfather, Prince William said Philip would remove the lid from a tube of mustard and get one of his grandchildren to hold it in between their hands.
“And then he’d squish your hands together to fire the mustard onto the ceiling,” he said.
“He used to get in a lot of trouble from my grandmother for covering most of the places we had lunch and things with mustard on the ceiling.”
Prince Philip died at Windsor Castle on 9 April, aged 99.
Prince Philip: The Royal Family Remembers features interviews with all four of the Queen and Prince Philip’s children, as well as their adult grandchildren and members of the duke’s staff.
Other grandchildren, Peter Phillips and Zara Tindall, also recalled the messy mustard game.
“I can’t remember exactly what he says but he ends up slamming your hands together.... It goes all over the ceiling,” Zara said.
Peter added: “I actually think the marks are still there.”
Recalling the duke’s fun-loving nature, William and Prince Harry told the BBC that both the Queen and Philip would enjoy it if things went amiss on royal engagements.
“My grandfather loved things when they go wrong,” William said.
“Both my grandparents love that because you can imagine, they’ve lived a life where everything has to go right the whole time and so when things go wrong, they both chuckle an awful lot.
“Everyone else gets mortally embarrassed. They love it,” he added.
Harry said the couple would be “excited” by the prospect of what could go wrong.
“The two of them are going ‘Well I wonder if something’s gonna go wrong this year? How exciting’,” he said.
He described the Queen and Philip as “the most adorable couple”, but said that he knows his grandmother will be “OK” without him.
“More than anything I miss his humour but I miss him, I miss him more for my grandmother because I know how incredibly strong she was with him there. I also know that she’s gonna be OK without him,” Harry said.
Prince Philip’s funeral was held on 17 April at Windsor Castle. The duke would have celebrated his 100th birthday in June.
Noting his grandfather’s love of cricket – he served two terms as president of the Marylebone Cricket Club – Harry said Philip has a “fantastic innings” and scored a six, but “didn’t actually want to get to a century”.
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