Damon walked the red carpet at the premiere of his new drama thriller, Stillwater, on Monday, at the Rose Theater at Jazz at Lincoln Center in New York, and he opened up to ET's Rachel Smith about how he got choked up earlier this month after the successful Cannes debut.
"I mean, I turned to the director [Tom McCarthy] and I was like, "I'm thinking I am getting old because I am really emotional right now,'" Damon said with a laugh.
Damon's film played at the prestigious film festival on July 8, and was met with a standing ovation. The actor was spotted getting teary-eyed from the applause and the gravity of the circumstances.
"I think it was just being in a theater again with everybody, just a thousand strangers. And that feeling, I just love it," he explained. "I just missed it."
Damon said that, after "sitting on my couch in sweatpants for a year and a half and just watching stuff that way" it was nice to sit with a crowd and experience them seeing a project you've poured your time and attention into.
"It is good to come back here and it's good to come back and see things with other people," Damon said.
In Stillwater, Damon plays Bill Baker, an oil worker from Stillwater, Oklahoma, who travels to France when his estranged daughter Allison (Abigail Breslin) is charged with murdering her friend while studying in Marseille.
Bill tries everything he can to help his daughter prove her innocence as time slowly run out, while contending with stark cultural differences and a complex and radically different French legal system.
In real life, Damon is a father as well, and shares four daughters with wife Luciana Barroso -- Isabella, 15, Gia, 12, and Stella, 10, as well as his stepdaughter Alexia Barroso, who Damon gushed, "She was 4 when I met her and is 23 now, I don't know how that happened!"
Damon posed on the carpet with Alexia, who dressed to the nines for the occasion, and they were joined by his mom, Nancy Carlsson-Paige, and stepdad, Doug Kline.
Despite being an A-list movie star with a laundry list of hit films and accolades under his belt, Damon explained that his celebrity really doesn't have much of an impact on his kids.
"None of that really invades my regular life," Damon shared. "I am just dad. You know what I mean? That is just how it should be."