United Kingdom, Sept. 28 -- 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 ...