Actor Matt Damon's next project could be wedding plans.

The Good Will Hunting hunk announced last week at a star-studded gala that he and Odessa Whitmire, Ben Affleck's former personal assistant, are getting hitched.

The couple showed up arm-in-arm to a New York benefit hosted by actor-director George Clooney and Miramax producer Jon Gordon on Wednesday night and soon broke the news to friends as Whitmire's 3-carat diamond sparkled.

Damon met Whitmire, 27, in September 2001, when Affleck, Damon's longtime buddy, checked into rehab.

While Damon has never had trouble talking about his affection for Whitmire, he and his rep have shot down months of engagement rumors.

"I'm not engaged," Damon, who dated Minnie Driver and Winona Ryder, told The Post this past June.

"I have no plans to get married or have kids. I've got my nephews. That's about all the responsibility I can handle right now," he said.

Sources told Page Six a month ago the couple were tying the knot, but Damon's rep "[didn't] know anything about that."

But now Damon has followed Affleck's engagement to Jennifer Lopez with his own.

Before the end of Wednesday night's benefit, which raised over $200,000 for the Kenny Gordon Foundation, Damon, 32, said he was retiring his black book, buxom babes and staunch bachelor ways.

While Damon was tight-lipped about when or where the marriage will happen, one source said the ceremony wouldn't take place until Affleck and Lopez exchange their vows - which is expected to happen sooner than later.

Last month, Lopez said in a televised interview that Affleck got down on one knee, popped the question and she answered, "Yes." Affleck and Lopez met last year on the movie set of Gigli.