|Brad Pitt and George Clooney|
The 'Descendants' star is notorious for playing practical jokes on his co-stars and joked he is preparing a massive gag that could have serious repercussions for his close pal.
Speaking on 'Inside the Actors Studio', he said: "I have done some horrible things to people. Truly, truly horrible. I owe him, so I'm getting him.
"I'm working on one right now for Brad Pitt. It might end his career.
"I've been working on it for two years. I'm not going to tell you what it is, but just know, I got it."
However, there could be a long wait before George executes his prank as the 50-year-old star - who is currently dating former WWE wrestler Stacy Keibler - recently admitted some of his jokes have "taken years" to pull off.
More celebrity gossip on IrishCentral Irish tsunami 'quite possible' warns experts after earthquakeUS Census reveals important new information on Irish Americans
He added: "You set a bit of a trap and then you watch it slowly unfold. I've had ones that have taken years."
George's scheme is unlikely to upset Brad, 48, as the 'Moneyball' actor is also a fan of jokes, and the 'Ides of March' recently described him as a "brutal" prankster.
He said: "My friends are rough on me. Brad Pitt's brutal, and Matt Damon.
"My friends used to change my outgoing phone message all the time. This was the old days, when you had a phone machine. They would change the message to something horrible and there was nothing I could do to change it back. That was always brilliant."