Casey Affleck had "no doubt" Matt Damon was going to be a massive star.

The 51-year-old actor, who lived with older brother Ben Affleck and their childhood friend while they were chasing their acting dreams, has reflected on the early promise his pal showed at a young age.

Speaking at Zurich Film Festival, he said: "We all had the same theatre teacher … and lots of actors came through this one theater department.

"We were in a big public school, and we just had this great theatre teacher, and he made kids fall in love with theatre and acting.

"Matt was always a bit of a showoff. [He was] outgoing and would do talent shows and stuff. And there was no doubt where he was headed, but the rest of us were trying to figure it out."

Casey and Ben were both encouraged to act by their parents - who divorced over 40 years ago and both passed away this year - with their father working as a stage manager, meaning they both grew up around the theatre.

Casey, who also appeared in the likes of Good Will Hunting and Ocean's Eleven earlier in his career, insisted he, Ben and Matt are "all very different in a weird and very obvious way".

He explained: "Matt is a super talented actor. He's a funny case because he's a very talented actor who has a kind of movie star persona, a matinee idol appeal, at the same time, which Ben and I don't really have.

"Ben seems more like a movie star and has leaned into the leading man thing right from early on."

In the past, Casey has been referred to as a Hollywood outsider, and it's a label he's grown to accept,

He said: "I saw that and I thought, 'Man, I'll forever be thought of as an outsider, no matter what I do.'

"You can win an Oscar, or you can do a big giant studio movie, and I think the public just thinks of people one way, and then it takes a lot to change that.

"I was sitting with it for a second, and I thought, 'Am I crazy? I love that.' I don't want to be an insider. I love being an outsider. I would much rather be an outsider in Hollywood than be an insider in Hollywood.

"I don't think it's a great culture. I don't love the movies that are made by Hollywood. I don't love the system of Hollywood, and I'm very happy being thought of as an outsider."