The Friends star is one of the famous faces taking part in the forthcoming celebrity series of the hit Channel 4 show, in aid of Stand Up To Cancer.
In an interview with The Mirror, Prue revealed she believed the US actor would be more like his sitcom character Ross Geller, and was surprised to see him taking the competition so seriously.
“Well, he must have been the most famous person we had in the tent. And I was very excited about it,” she said.
“What I was surprised about, though, was I thought he’d behave like he behaved as Ross, he’d be like he was in Friends. But he was actually very concentrated and didn’t want to talk to anybody.”
“He just wanted to get on baking and he badly wanted to win,” she continued, adding that David eventually “loosened up after a while”.
In an interview with Closer magazine, Paul previously named the Friends actor as the celeb he’d most like to see on Bake Off after “he let us down at the last minute” just before filming was due to start.
The Great Celebrity Bake Off in aid Stand Up To Cancer begins on Sunday 19 March at 7.45pm.