GEORGE CLOONEY 'FAT' PRANKED MATT DAMON DURING 'MONUMENTS MEN' SHOOT

Matt Damon and Jay Leno (R). Credit: Paul Drinkwater/NBC/NBCU Photo Bank via Getty Images

He's tricked Sandra Bullock into jumping into a pool solo. He made Ryan Gosling look like he peed himself on set. Now George Clooney has made co-star Matt Damon think he was getting a little too large around the middle in a during filming of 'The Monuments Men.'

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Matt Damon admitted he fell for the notorious actor's joke without even knowing it while appearing on The Tonight Show with Jay Leno in the US.

Leno quipped, "I know [George's] a huge practical joker... Did he get you with anything?"

"I read, finally -- which answered a lot for me -- that [George] had been taking...my pants in by about an eighth or a sixteenth of an inch every couple of days," Matt said. He continued, "[George] had said 'We're gonna get in shape,' and I said, 'Yeah, I'm gonna get in shape,' so I was working out, and the pants just wouldn't [fit]... I was like, 'This can't be!'"

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While Matt was struggling to deal with his pants situation, he suffered in silence, not wanting to admit the situation to George, who also directed the film.

"I never said anything to him of course," Matt laughed, adding, "Which he probably loved even more."

'The Monuments Men' is in local cinemas on March 13.