Throughout George Clooney's career, he's been able to get away with pranking some of Hollywood's biggest names.
But at least two major celebrities recognized, or at least suspected, his shenanigans in recent years.
Clooney pulled fast ones on at least three co-stars from the 2014 film "The Monuments Men."
While hosting Bill Murray at his home, Clooney hid 11 pounds of gravel in his suitcases.
Clooney then reveled in watching the "Caddyshack" star lug them around in confused fashion.
Another "Monuments Men" co-star, Matt Damon, got conned with help from the wardrobe department.
Clooney convinced a "Monuments Men" wardrobe staffer to make some sneaky alterations that would mess with Damon's mind.
"When we were about to start shooting, [Damon] said he wanted to lose a couple of pounds," Clooney recalled at a 2014 press conference.
Damon confessed, "So stupid of me."
Replied Clooney with a grin, "You should never have told me that."
When Damon returned to Los Angeles in between shoots, Clooney added, the prankster persuaded a "Monuments Men" tailor to take in Damon's costumes "half an inch" at a time.
"I never really discussed it with [Damon]," noted Clooney, who then turned to his co-star at the press conference. "I found out only a few days ago that it really disturbed you."
Damon said he preferred a different prank played on Clooney's father, Nick Clooney, whose character walks into the light of a church at the end of the film.
Clooney detailed that prank's payoff in a separate interview with CNN.
"I screened this for my dad in Italy," Clooney recalled. "It was a rough cut of the film. And the first thing that comes up [on the screen after that scene] is 'In loving memory of Nick Clooney.' And he's like, 'What the hell?!'"
Clooney nailed Damon again while employing the same fake-stationery technique used to tweak Brad Pitt and Meryl Streep.
(Check out Part 2 of Circa's Clooney pranks series for more details about that execution.)
For the stationery sequel, Clooney got an assist from fellow prankster Jimmy Kimmel, who'd given Clooney some blank cards with Damon's name on them.
The beef began at the 2014 Golden Globe Awards, when hosts Amy Poehler and Tina Fey's monologue jokes included barbs at Damon and Clooney's expense.
Addressing Damon, Poehler scoffed, "On any other night, in any other room, you'd be a big deal, but tonight, don't take this the wrong way, you're basically a garbage person."
Minutes later, Fey described the film "Gravity" as "how George Clooney would rather float away into space and die than spend one more minute with a woman his own age."
Days later, Clooney told "Access Hollywood" that the hosts' jokes had "poked the bear."
But the nature of Clooney's revenge was not revealed during that "Access Hollywood" interview.
It would, however, be explained in full while Clooney appeared as a guest on "Jimmy Kimmel Live" in May 2015.
During that appearance, Clooney admitted Fey's "Gravity" one-liner was a "great joke," adding, "I was glad I wasn't there [at the ceremony] at the time."
In response to the monologue mockery, Clooney told Kimmel, "I sent notes to Tina and Amy from 'Matt' saying, 'You know, the George joke was OK, but, y'know, my daughters saw the joke you did about me ... and it really hurt me.'"
Fey and Poehler responded cautiously.
To be on the safe side, one delivery of flowers was addressed to Damon, apologizing if, indeed, his feelings were hurt.
Fey and Poehler's alternate reply pegged the situation accurately. Laughing, Clooney told Kimmel that addendum read, "We think that this is from George Clooney. We're grown f**king women. F**k you."
Fey and Poehler also reportedly called themselves "grown-ass, professional comedians."
George Clooney's pranking shenanigans have been going on for decades. Learn about his earliest A-list practical jokes in Part 1 of Circa's series.
Who got the best of whom in the Clooney-Fey/Poehler prank? Vote in Circa's poll and explain your answer in the comments section!