Watch: Matt Damon sings “Sweet Caroline” with Jimmy Fallon during Tonight Show appearance

"It's a singalong," Damon said about his choice of song.

Good times never seemed so good at the Tonight Show on Wednesday night, as Matt Damon gave an impromptu performance of “Sweet Caroline” alongside host Jimmy Fallon.

Early in the interview, Fallon brought up a time he and Damon were at a children’s party together. The host said he and Damon got the kids dancing during the karaoke part of the party.

“I was kind of freaked out, thinking ‘What song should I do?’” Fallon said. He recalled how Damon came up with the idea for them to sing “Sweet Caroline.”

“It’s a singalong,” Damon said about his very Boston choice of song. “That alleviates the pressure. Then everyone sings along, and then you wrap,” he said.

Damon stopped by the Tonight Show to promote his new movie “The Instigators,” in which he co-stars with fellow Cambridge native Casey Affleck.

“It’s a heist movie,” Damon said in the interview. “But if the A-team isn’t available, and you can’t get the B or C team either, you get us.”

The movie is set and filmed in Boston. Bova’s Bakery in the North End, famous for being open 24/7, temporarily closed in 2023 so it could be used as a set.