David Schwimmer made an unexpected discovery on the set of his directorial debut, the romantic comedy Run Fat Boy Run - Thandie Newton has decidedly wicked streak. The mischievous British beauty turned out to be the unexpected prankster of the cast, with co-star Simon Pegg the butt of many of her jokes.

And at the premiere for the flick - which follows Simon's attempt to win back the love of the pregnant fiancée he jilted ten years before by running a marathon - the camaraderie and high jinks continued. And the Friends star, who spent a year in the British capital lensing the movie, had an enthusiastic greeting for Zimbabwe-born Thandie and Matthew Fenton, the little boy who plays her on-screen son.

Among the Crash actress' more memorable tricks were putting cellophane on the loo seat and exchanging Simon's mineral water for something slightly stronger, making him pull a face when he discovered the switch during promotional interviews.

The fun-filled air on set also helped cement friendships it seems, with the American actor-turned-director finding a new pal in Simon, based on their shared sense of humour. "I'd find some things so funny that I'd totally screw up a take because I was choking with laughter," he confessed.

Photo: © Alphapress.com
Director David says he had a ball filming the new romantic comedy Run Fat Boy Run. At the London premiere he was reunited with Thandie, who contributed to the fun with her on-set pranks, and Matthew, who plays her son in the flickPhoto: © Getty Images
Photo: © Alphapress.com
The former Friends star also became close pals with Simon Pegg, after discovering that they share a similar sense of humourPhoto: © PA