David Walliams was so impressed by one of the acts on Britain's Got Talent that he jumped up on stage and joined them.
The Little Britain star said his new role "felt natural straight away" and he tried to make show supremo Simon Cowell laugh as well as the audience.
He said: "If Simon didn't find me funny, it wouldn't work. The audience love Simon but because he's so successful they want to see him teased a bit as well. So I'm really enjoying winding up Simon. It's fun."
David, who admits he is "a shameful exhibitionist", said he enjoyed the chance to get up on stage.
He said: "I was really excited by one of the acts so I went up on stage and joined them for a song. It was a bit like The Generation Game because I didn't know what I was doing, but it was fun."