Casey Affleck has joked that his brother Ben and childhood friend Matt Damon were trying to "relive their glory days" after the pair revived their Good Will Hunting roles for a live read on Friday.
Batman star Ben Affleck and Jason Bourne star Damon won an Oscar in 1998 for their screenplay about a maths genius working as a janitor at MIT until his life is turned around by a therapist, played by the late Robin Williams.
The pair revived their roles for a live reading of the script in New York - to the bafflement of Ben's younger brother Casey, who also starred in the 1997 film.
Arriving at the BFI London Film Festival premiere of his new movie, Manchester By The Sea, he joked to the Press Association: "What a weird thing to do.
"I came here so I wouldn't have to do it. I can't imagine what that was like and I look forward to seeing a videotape of it," before adding: "I guess they do it all the time, those live reads, but they are trying to relive their glory days I guess."
In his new film, Casey plays a man grieving the loss of his brother when he finds out he has become the guardian of his nephew.
The film was a hit when it premiered at the Sundance Film Festival, where it sold to Amazon Studios for a reported 10 million dollars (£8 million) after a bidding war, and has already sparked awards chatter.
Casey said he hopes the glowing reviews help the micro-budget film find a wider audience.
He said: "It's great to have positive feedback and to have people like it, it means a lot and I've grown to be less cynical than I used to be and it's great when people like movies like this that need a lot of help to get an audience.
"It was a beautifully written, very complicated role, a very, very hard role.
"I like challenges, I like to be pushed, I like to be not quite up to the challenge and have to find my way there, and this script had all of that. It's a nice reminder that movies can still really affect people and move people.
"I think everyone that sees this has responded with a lot of emotion. We are so often consuming media in 30 seconds - little bites on our phones - and movies like this keep the whole cinema thing going."
Dawson's Creek star Michelle Williams, who plays Casey's estranged wife, added: "When movies are this small, they are barely scraped together.
"Other people were not keen to make a tiny little movie about grief and when you sign on for a movie like this, never in a million years do you think it will come to this dazzling end.
"You're just glad it's getting made."
Manchester By The Sea will be released in UK cinemas on January 13 2017.