The first-time host called the awards show "the weirdest TV finale since Lost."
"Except for the end, it was a lot of fun," Kimmel told his audience. "It went very well, we were chugging along, and then all of a sudden out of nowhere it turned into one of those Maury Povich paternity test shows."
Kimmel saw the whole thing go down from the audience, where he was in position for a pre-planned bit to close out the show, sitting next to -- who else? -- Matt Damon.
"So we're sitting there and you just kind of figure, well, the host'll go on stage and clear this up," Kimmel said. "And then I remember, oh, I'm the host."
"I want to make no mistake about it," Kimmel noted. "Whatever confusion there was about who won, Matt Damon lost [for producing Best Picture nominee Manchester by the Sea]. He was a loser. He is a loser."
After the commotion had died down, Kimmel said that some people immediately assumed he was responsible for giving Beatty the wrong envelope as a final prank, an assumption he was quick to correct. "If I had pulled a prank," Kimmel said, "I wouldn't have just had the wrong winner's name on the envelope. When they opened it, there would have been, like, a Bed Bath & Beyond coupon in it."
Check out Kimmel's monologue from Monday night to get more behind-the-scenes secrets from Hollywood's biggest blunder night.