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Casey Affleck has won his first-ever Academy Award — and he forgot to give props to some major people in his life.

The Manchester by the Sea star took home the Oscar for Best Actor, winning for his gut-wrenching portrayal of a man tasked with raising his teenage nephew after the death of his brother.

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Affleck first thanked fellow nominee Denzel Washington for being “one of the first people who taught me how to act,” adding, “I just met him tonight for the first time.”

“And to all the other nominees who did great work, I’m proud to be in your company because you’re very brave and I admire what you do,” said Affleck, 41. “I’m only here really because of all the talents and goodwill of so many people, they’re impossible to name. But most of all, Kenneth Lonergan who made this part, and without this part and without his writing I wouldn’t be here for sure and, well, he directed it.”

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“Man I wish I had something bigger and more meaningful to say, but I’m just really proud to be a part of this community in general. I look at all of you, I have this whole year, I’m just dumbfounded that I’m included. It means a lot to me.”

After stepping away from the podium, Affleck quickly realized — thanks to a call from his 12-year-old son — that he hadn’t given a shout-out to his children. “My head was completely blank with the shock of winning an award,” he explained to reporters backstage. “I didn’t thank my children, which is something I’ll probably never live down. Three seconds later my phone rang and my son said, you didn’t even mention us! And my heart just sank.”

But there was a silver lining when it comes to family, as Affleck’s brother Ben was moved to tears at the chance to celebrate his younger sibling’s win in the audience.

“It was very moving. My brother, to have him there, it was a nice moment. I saw those tears and I thought, maybe I’m just not making a good speech and he was really disappointed!” Affleck said, adding, “Not to brag, but I think we’re the only two brothers to win Academy Awards.” (In fact, directors Joel and Ethan Coen share eight Academy Awards between them, and composers Alfred and Lionel Newman’s tally hit 10 during their careers.)

He added of Ben, 44: “I‘ve learned from him because he’s been through a lot in this business, ups and downs and been under-appreciated, and he’s proven how great he is. I definitely have had an advantage getting watch him the tricky waters of being famous. I’ve learned a lot from him.”

And it was all celebrations after the show. Affleck attended the Vanity Fair party with Lonergan, arriving late into the night and staying until the very end.

Affleck had long been considered the Oscar front-runner, thanks to his powerful performance in Lonergan’s drama, but many had objected to his nomination because of sexual harassment allegations dating back to 2010. Affleck has repeatedly denied the allegations, and the claims were settled out of court. The 41-year-old actor did not mention the claims during his acceptance speech.

Check out PEOPLE’s full 2017 Academy Awards coverage and complete winners list!

Affleck notably beat out Washington for Fences, who had made a late push for his third Oscar — and even won at the Screen Actors Guild Awards last month. Other nominees in the category were Andrew Garfield for Hacksaw Ridge, Ryan Gosling for La La Land, and Viggo Mortensen for Captain Fantastic. He was previously nominated for Best Supporting Actor in 2008 for his role in The Assassination of Jesse James by the Coward Robert Ford.

RELATED VIDEO: The 2017 Oscar Nominees, By the Numbers

In all, Manchester by the Sea earned six nominations, including Best Picture, Best Director for Lonergan, Best Supporting Actor for Lucas Hedges and Best Supporting Actress for Michelle Williams.

The 89th Annual Academy Awards, hosted by Jimmy Kimmel, are airing live from Los Angeles on ABC.