Matt Damon says Ben Affleck is 'fantastic' after rehab

Ben is "Mr. Mom-ing it right now," he said.

During an appearance at CinemaCon in Las Vegas to promote his new film, "Suburbicon," on Tuesday, Damon told "Entertainment Tonight" that Affleck is "with the kids now" and "couldn't be happier."

Affleck is "lucky" to be surrounded by such a solid group of guys, according to Damon. "I have a good group of friends ... we always keep track of each other and look out for each other."

Earlier this month, Affleck, 44, announced that he successfully completed a rehab program.

"I want to live life to the fullest and be the best father I can be," he said in a Facebook post earlier this month. "I want my kids to know there is no shame in getting help when you need it, and to be a source of strength for anyone out there who needs help but is afraid to take the first step."