With their new movie, The Last Duel, Damon, 51, and Affleck, 49, are reuniting as costars and co-writers for the first time since the childhood pals struck Oscar gold and launched their A-list careers with 1997’s Good Will Hunting.
“Being able to share that incredible experience and lean on each other through it all cemented their friendship,” says an insider. “They’ve been supporting each other onscreen and off, and through a lot of ups and downs, ever since.”
“They’re both wary of the pitfalls of fame," an insider says of the pals, who grew up together in Cambridge, Mass., "and promised to keep one another grounded."
But the pals hit a bump in 2002 when The Way Back actor began dating his Gigli costar Jennifer Lopez.
“All the attention went to his head, and when Matt voiced his concerns about what it may do to Ben’s career, they had a falling out,” spills the insider. “They didn’t speak for months, but Ben finally came to his senses and realized Matt was only looking out for him.” (Affleck and the former Fly Girl called off their engagement in 2004.)
“But he’s now their biggest cheerleader because he’s gotten to know Jen all over again,” explains the insider. “Matt can see how happy she makes Ben.”
As OK! previously reported, Damon praised the lovebirds during an interview in July, telling Extra: "I’m just so happy for [Affleck]. He’s the best. He deserves every happiness in the world. I'm glad for both of them."
The Stillwater star — who’s supported Affleck throughout his struggles with alcohol over the years — “will always be protective of him, and Ben is beyond grateful,” adds the insider. “These guys are bonded for life!”