Matt Damon Says George and Amal Clooney Will Be 'Great Parents'

"I've never had twins. He has it coming," he joked.

The former "Good Will Hunting" star reacted "'Are you out of your mind?! Don't tell anybody else! Don't you know the 12-week rule?'"

Clooney, 55, followed up four weeks later to tell Damon everything was fine.

"[Clooney] never even said, 'Don't tell anybody,'" Damon added. "We just know that's their incredibly wonderful news, and it's theirs to share with the world."

Damon did have some concern for the fellow Oscar-winner -- the fact that he and his wife are expecting twins.

"I've never had twins. He has it coming. I had them one at a time you know, and that was plenty," he told ET. "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."