George Clooney Pranks Matt Damon, Makes Him Think He Got Fat

George Clooney pranked Matt Damon on the set of their latest movie "Monuments Men," but the actor didn't realize what had happened until after the movie had already wrapped up. Damon admitted on the "Tonight" show with Jay Leno that Clooney got him good.

George Clooney's prank for Matt Damon had to do with the "Good Will Hunting" star's wardrobe. Every so often, 52-year-old Clooney would freak Damon out by secretly altering his clothes- even worse, the actor would mention all the exercise they were getting, making Damon feel worse about "gaining" weight.

"He said, 'Oh we're going to get in shape,' and I said, 'Yeah we're going to get in shape,' so I was working out and my pants [were getting tighter] and I was thinking, 'This just can't be,'" Damon said.

It took until after the movie had wrapped for Damon to realize what had happened: Clooney, who is known for being a prankster, had been altering his pants little by little.

"I read, finally, which answered a lot for me that he'd been taking my wardrobe in, my pants in by about an eighth or a sixteenth of an inch, like every couple days," he said.

Clooney admitted in November that this is his favorite trick to play on his co-stars, which usually sends them into a dieting craze because of the mystery weight they're gaining.

"I never said anything to him which, of course, he probably loved even more," Damon told Jay Leno.

This isn't the first time Damon was suspicious of Clooney's notorious pranks. A few years ago he couldn't fit into a suit for a function, and he thought he might be the victim of a practical joke.

''My immediate thought was that my buddy George Clooney had hired someone to get into my closet and cut down my clothes. I seriously thought that - until my wife said, very gently, said 'Do you think it might be that you've put on some weight?'''