Matt Damon is really good at keeping secrets!
ET's Kevin Frazier sat down with the 46-year-old actor at the junket for his new film, The Great Wall, in Los Angeles on Thursday, where he opened up about his good friend, George Clooney's, baby news -- and how he was able to keep such a big secret.
WATCH: George and Amal Clooney Are Expecting Twins!
"[Clooney] never even said, 'Don't tell anybody,'" Damon revealed. "He told me [and] I'm sure he knew I'd tell my wife [Luciana Barroso]. My wife wrote to Amal immediately, 'Congratulations.'"
"The way to not let a secret go out is you don't tell anybody," the actor continued. "It's not rocket science and we just know that's their incredibly wonderful news and it's theirs to share with the world. My wife and I talked about it with them but there wasn't anything to share with anybody else."
News broke on Thursday morning that Clooney and his wife, Amal, were expecting twins. Julie Chen confirmed Amal's pregnancy on The Talk, adding that the babies are due in June.
As for the advice Damon offered his pal, he says Clooney "has it coming."
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"I've never had twins. He has it coming. I had them one at a time you know and that was plenty," the actor revealed.
"Look, the two of them, they're just great people and they're going to be great parents. It's going to be a huge challenge, I mean, one baby cries, wakes the other up. It’s going to be on in that household," he added, "[but] he doesn't sleep a lot anyway. He'll be alright. I'm serious, he's got a hell of a work ethic."
Damon opened up more about the baby news to ET Canada's Matte Babel, revealing when Clooney first announced the news.
"I was working with him last fall, and he pulled me aside on set, and I mean, I almost started crying. I was so happy for him. And I was like, 'How far along is she?' and he goes, 'eight weeks,'" the father of four recalled.
EXCLUSIVE: George Clooney Jokes About Second Anniversary to Wife Amal: 'And They Said It Wouldn't Last'
"'Are you out of your mind?! Don't tell anybody else! Don't you know the 12-week rule?'" Damon said he shouted at his Oceans Eleven co-star. "Like, of course he doesn't. 'Just shut up, man.'"
It seems Clooney took Damon's advice, only confirming, "We're good," four weeks later.
"I'm thrilled for him. She's amazing. He hit the jackpot, just on every level. She is a remarkable woman," he gushed of Amal. "They're going to be awesome parents. Those kids are lucky."
The Great Wall hits theaters on Feb. 17.
WATCH: Amal Clooney Turns 39, Celebrates With Husband George in Spain