Casey Affleck Reveals His One Oscar Acceptance Speech Regret

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With his new Academy Award in hand, Casey Affleck admits that his "heart sank" just moments after finishing his acceptance speech.

"I didn't thank my children, which is something I'll probably never, ever live down," Affleck told reporters backstage at the Oscars on Sunday. The 41-year-old star took home the award for Best Actor for his gut-wrenching role in Manchester by the Sea, beating out Denzel Washington, Andrew Garfield, Ryan Gosling and Viggo Mortensen for the honor.

"Three seconds after I left the stage, my phone rang and my son said, 'You didn't even mention us!' and my heart sank," Affleck said after his win. "That's probably the most significant thing I could have said."

RELATED: 'Manchester by the Sea' Director Kenneth Lonergan on Mel Gibson and the 'Special' Year of Movies 

Affleck did pay tribute his brother, Ben Affleck, during his time at the podium, after being teased earlier this awards season for neglecting to thank him during his Golden Globe acceptance speech.

"It was very moving and obviously to have my brother there, yeah, it was a nice moment," he said of the Oscars. "I saw those tears and I thought maybe I'm just not having a good speech and he's really disappointed, but I think he's probably really touched."

The elder Affleck, 44, has won two Oscars over the course of his career, though neither are for acting. He shared his first win with Matt Damon in 1997 for the Good Will Hunting screenplay. In 2012, he was awarded a Best Picture trophy as a producer on Argo, for which he had also served as the director and star.

"We just hugged," the Manchester actor said on Sunday. "I've learned a lot from him because he's gone through ups and downs ... It's been an advantage to be able to watch someone you love navigate the tricky waters of being famous, so I've learned a lot from him."

Manchester by the Sea scored one more Oscar on Sunday night, with Kenneth Lonergan receiving the award for Best Original Screenplay. Coincidentally, that category was presented by Ben Affleck and Matt Damon.