Queen Elizabeth and Prince Philip "loved" things going "wrong" on royal engagements.
The monarch and her late husband - who died in April aged 99 - couldn't help but see the funny side when things didn't run smoothly and would find it "exciting" if something didn't go according to plan.
Speaking in documentary 'Prince Philip: The Royal Family Remembers', which aired on Wednesday (22.09.21) on BBC One, Prince William said of his late grandfather: "He enjoys playing practical jokes and foolery. He loved when things go wrong.
"My grandparents love when things go wrong. You can imagine, they have lived a life where everything has to go right the whole time, so when things go wrong, theory both chuckle. Everyone else is mortified embarrassed. They love it."
And in a separate interview, the Duke of Cambridge's brother, Prince Harry, agreed.
He said: "I think there is an imbalance of there is everyone doing everything like, 'The Duke of Edinburgh is coming, let's make sure we get everything absolutely right. Remember every single year we've got it right, let's do that.'
'But the two of them are going, 'I wonder if something is going to go wrong this year. How exciting.'
"What I remember now is the expressions on his face to the things that went wrong. He would just sit there completely calmly and just watch us run by."
And Philip's grandchildren recalled how the Duke of Edinburgh used humour to put people at ease and was very quick-witted.
Princess Beatrice said: "I think he has a very good observational humour but you've really got to be quick, you've really got to be paying attention.