Thus, when E! News caught up with the Martian star at a dinner for the film at the Toronto International Film Festival on Tuesday, we couldn't help but ask: Which brother does he prefer working with?
Damon had no hesitation in answering. "Not to throw him under the bus, but Ben is much easier to work with," he told us. "I mean, with Casey and I, we've done a bunch of movies together. We did [a play] in London 14 years ago, and I'll never forget the day we were on-stage rehearsing he told me how I should play my part."
Ron Galella, Ltd./WireImage
Though he had a hard time accepting it, Damon knew Casey's advice was actually really helpful.
"It was one of those things where I had to kind of take his suggestion," he said, admitting to giving him grief about it. "But I had to kind of hold onto my pride."
Despite choosing Ben, Damon couldn't help but praise Casey. "He's a really gifted actor and writer," he said, before laughing. "But he can be frustrating!"
Meanwhile, Damon and Casey's new film Machester by the Sea will be released later this year. It focuses on an uncle (played by Casey) who has to take care of his nephew after the young boy's father dies.
Needless to say, the plot is bound to be heartbreaking, and Damon admits it's a tearjerker.
"I never made it through the screenplay without crying," he told us. "It was one of those screenplays, it was just magnificent."
Manchester by the Sea hits theaters November 18.