"William was following her round like a lost puppy as she went around the room, chatting away and dancing."In the end, he just grabbed her and took her on to the dancefloor where they started doing some rather close dancing.
They couldn't keep their hands off each other but William didn't care that people were looking.
That's why she wanted to be out with her girlfriends and even flirted with other guys at clubs.
"Kate felt she was never able to do those things when she was with William."Now the ball's in her court.
They then left the party early to go back to William's barracks.
"William invited Kate down for the party," a source said.
Although she has been happy to smile for photographers while emerging from London nightclubs since the break-up, the constant media attention during her four-year relationship with William sometimes proved difficult for her.