Wearing yellow hotpants, sequins and roller skates, the royal sweetheart showed her fun-loving side at the London party in memory of an old schoolfriend.
Revellers, including Kate's sister Pippa and Richard Branson's daughter Holly, were supporting a fundraising appeal for "Tom's Ward" at Oxford Children's Hospital. The new unit is to be named after Tom Waley-Cohen, a friend of Kate's from Marlborough boarding school, who died of bone cancer in 2004, aged 20.
Tom's brother Sam said the event was intended to "reflect the lighter side of life; very much like Thomas was himself". He added: "We wanted to do something fresh and new; something that would be fun and a bit tongue in cheek."
He also heaped praise on Kate for her help in organising the event. "She's been fantastic in using her contacts to get people along - she has persuaded loads of people to commit."