Ben Affleck has some beef with his little brother Casey Affleck.

After excepting his Golden Globe for best actor for his role in Manchester By the Sea on Sunday, Casey thanked a long list of people for the award, including his costars, filmmakers and even producer Matt Damon — but he failed to mention one person in particular: his older brother.

“He thanked a s—load of people, I gotta tell you the truth,” Ben said on Monday while appearing on Jimmy Kimmel Live! “I was a little taken aback. That’s not the kind of thing I would do.”

In fact, Ben did thank Casey when he accepted the Academy Award for “Good Will Hunting” in 1998, even calling him “brilliant.”

But just because he was left out of the acceptance speech that doesn’t mean Ben wasn’t cheering him on during the award show.

He broke into a fist pump when Casey’s name was announced as the winner, and also looked emotional and proud as he heard Casey’s acceptance speech, even rushing backstage to hug him.

While discussing awards season, Kimmel predicted that Casey, 41, would take home the Academy Award for best actor, and how he believed the Affleck siblings could become the first brothers to win in separate categories, since Ben already has two Oscars to his name.

“It would be historically the first time brothers would win something separately, and not just the brothers winning, but this will be the very first time someone would win an Oscar who didn’t brush his teeth from ages 10-14,” Ben shared.

Credit: Todd Williamson/Getty Images for Amazon

“It will be the very first time that someone, who wins an Oscar, who pulls his pants all the way down at the urinal, most Oscar winners don’t do that,” the older brother continued. “Well, the first person to win who is scared of butterflies … not only that he would the first to win that used to touch himself watching the Vicky the Robot from Small Wonder.”

And last but not least? “The very first person to win an Academy Award who asked his brother if Back to the Future was a true story,” he concluded.