While chatting with Extra at the premiere of his latest film Stillwater in New York City on Monday evening, the 50-year-old actor talked about Affleck, 48, and his rekindled romance with Jennifer Lopez.
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When asked to share his thoughts on the pair's relationship, Damon told the outlet, "I'm just so happy for him."
"He's the best. He deserves every happiness in the world," he added. "I'm glad for both of them."
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The current couple originally began dating in July 2002 after filming Gigli together. They got engaged that November before postponing their September 2003 wedding, just days before the date, and ultimately calling off their engagement in January 2004.
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getty (2) Ben Affleck (L); Jennifer Lopez
Lopez and Affleck made their new romance Instagram official on Saturday when they shared a passionate kiss in a photo she posted.
And source recently told PEOPLE that the pair "are madly in love" and "the loves of each other's lives."
Another source close to Affleck and Lopez noted that the Justice League actor is "very happy" with the singer, and that "she's wonderful for him," while an insider close to Lopez added, "They want to do everything they can to make this work."
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Of the connection between the two, the Lopez insider added: "Even though their split many years ago was devastating for Jennifer, she has never had a bad word to say about Ben."
"She believes that it just wasn't meant to be then and feels like they've been given a second chance," the insider continued.
The couple has been on a romantic yacht getaway to the Mediterranean and celebrated Lopez's 52nd birthday in St. Tropez on Saturday.