As the Middleton's get ready for Christmas, one thing Kate and Pippa are preparing for is their father's entertaining party tricks which include rather extravagant costumes.
Pippa told political magazine The Spectator the funny thing that happens every year during the holidays.
"My father has developed this funny tradition of surprising us at some point by appearing in fancy dress," she said.
"He buys a new costume each year and typically gets a bit carried away – a couple of years ago, he appeared in an inflatable sumo outfit."
The socialite said the tradition is "endearing, and only quite embarrassing," so Prince William should expect a lively celebration with his wife's family.