George Clooney 'Ashamed' of Prank Planned for Amy Poehler and Tina Fey

Amy Poehler and Tina Fey better watch their backs.

That was the message sent to the comediennes today by George Clooney who said there is more revenge to come for the Golden Globes hosts whose joke at the awards show last month mocking Clooney's taste in women was the hit of the show.

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"I'm doing something that I'm actually ashamed of, that's going to hurt them," Clooney said today on " Good Morning America." "I'll show you some photos later."

Clooney, 52, has already fired back at Fey, who described the Golden Globe-nominated "Gravity" as "the story of how George Clooney would rather float away into space and die than spend one more minute with a woman his own age."

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Clooney's first take on revenge at the Golden Globes hosts came at the expense of actor Matt Damon, whom Clooney stars with in their new film " The Monuments Men," and who was called by Fey and Poehler the "garbage man" among all the A-listers at the Golden Globes.

"I sent her a letter on Matt Damon stationery that said, 'Dear Tina, I may sound like a hypocrite because I laughed at the jokes about George and about Leo but they're kind of known for that and, you know, when you called me a garbage man, you know, it really hurt me and my kid calls me a garbage man now,'" Clooney explained.

When two "giant" fruit baskets showed up at Damon's front door a few days later, along with two notes, all three of Clooney's victims - Damon, Poehler and Fey - knew they had been had by Clooney.

The first note accompanying the fruit baskets to Damon was apologetic, while the second note made it clear that Fey and Poehler got the joke.

"If your note is part of some George Clooney prank, as I very strongly suspect it is, you A-list amateurs are going to have to step it the f- up. We are not some easily confused starlets here. We are grown-ass, professional comedians. Please accept this fruit as a token of our sincerity. Best wishes, Elizabeth Tina Fey, Amy 'Boston' Poehler."

The revenge via Matt Damon stationery was the second time in recent months that Damon has had to publicly admit that he fell victim to one of Clooney's infamous pranks.

While filming "The Monuments Men," Clooney, who also directed the film, instructed the wardrobe department to slowly take in Damon's pants, leading him to believe he was gaining weight while trying to get in shape for the film.

"Matt was rushing to lose weight, and I'd have the wardrobe people take in his uniform every day, so that no matter how much he was losing, the clothes felt tight on him," Clooney told Deadline in August.

There was no prank needed, however, when it came to casting Damon in the role as a soldier in a World War II platoon tasked to rescue art masterpieces from Nazi thieves, especially compared to corralling the film's other high-profile stars.

"I went to Australia for a day, which is a fun flight, to get Cate Blanchett," Clooney said on "GMA." "And Bill Murray came out to my house in Italy."

"And Matt, I think I just sent an email to Matt because we've worked together six times, so it was really easy," Clooney said.