Ben Affleck and Matt Damon Surprise Crowd During 'Good Will Hunting' Read in NYC

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And we have John Krasinski to thank for it.

Ben Affleck and Matt Damon have returned to their Boston roots!

Well, not really, but they did resurrect their Boston accents and Good Will Hunting roles for a special one night only live read of the script on Friday in New York -- and we have John Krasinski to thank for it.

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star hosted and served as guest director for the live reading, which benefited Film Independent, announcing to the crowd that the film was "unbelievably important to him," and that it was his lifelong dream to play Will Hunting.

Krasinski then introduced the cast, which included his wife, Emily Blunt taking on the role of Skylar, played by Minnie Driver, Daveed Diggs took on Casey Affleck's part as Morgan O'Mally, and Margot Martindale stepping in as Robin William's iconic character. Keegan Michael Key and Tom McCarthy also had roles.

It wasn't until later in the performance that Affleck and Damon appeared on stage, surprising the audience as they read their roles in the Oscar-winning drama.

"First John started reading Matt's part and you heard Matt off stage say, 'I have a problem with that,' and he walked out and sat down. So John moved over and sat in the seat for Ben's role, and he read two lines and then Ben walked out," an eyewitness tells ET. "People went nuts! Everybody screamed and jumped up with a standing ovation."

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While the night's cast had the dialogue down, they did go off script a few times to the delight of the audience.

"Every time Emily read Minnie Driver's part and her character and Matt's kissed John would make a comment like, 'They did not!'" the eyewitness recalled. "It was really fun! It was like an Oprah's Favorite Things reveal when they each came out, especially when Matt read the 'How ya like them apples' line -- the crowd went nuts!"

This wasn't the first time Krasinksi has been surprised by the Good Will Hunting actors.

In fact, Affleck showed up during Krasinski's interview on Thursday's Good Morning America.

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See the sweet surprise in the video below.