EXCLUSIVE: Ben Affleck on Valuing Matt Damon's Friendship and Why He Doesn't Give Advice to Brother Casey

Affleck opened up to ET at Monday's Live by Night premiere, acknowledging the people he relies on most when the going gets tough.

Ben Affleck opened up to ET at Monday's Live by Night premiere, acknowledging the people he relies on most when the going gets tough.

The Oscar winner's legendary bromance with childhood friend Matt Damon hit an all-time high last year with their playful feud in which they argued over who was better friends with New England Patriots quarterback Tom Brady. Damon even hacked into Affleck's Facebook to change the Live by Night star's profile picture, photoshopping his own face over Affleck's in a photo of Affleck with the Super Bowl champ.

PIC: Matt Damon and Ben Affleck's Bromance Was on Full Display at Guys' Choice Awards

This was all in jest, of course, to promote various philanthropic efforts, and Affleck got personal with ET on the Live by Night carpet, showing how much he appreciates people like Damon who have been by his side for most of his life.

"I can't tell you how valuable it is to have somebody who's been through things with you, ups and downs, who knows what your life experience is like, who can identify with that," Affleck told ET's Carly Steel. "It's an incredibly valuable friendship and it's very precious and so is my friendship with my brother. I don't know what I would do without those guys."

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Affleck's brother, Casey, won his first Golden Globe Award on Sunday for his leading role in Manchester by the Sea. When ET caught up with Casey at the awards show, he revealed that his brother rarely gives him advice even when he asks him for it. Ben told ET there's good reason for his silence.

WATCH: EXCLUSIVE: Casey Affleck Talks First Golden Globe Win, Jokes Brother Ben Displays His Awards 'In His Window'

"He doesn't need any advice," Ben said simply. "My brother is one of the smartest guys I know. He's savvy; he's smart; he's talented; he's thoughtful. He just knows what he's doing. He doesn't need me to help him."

Damon, who produced Manchester by the Sea, helped the brothers celebrate Casey's big win well into the night on Sunday, but as fathers, they still had a curfew to keep.

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"I had to get up and take the kids to school, so responsibilities were still calling," said Ben, who shares three children -- Violet, 11, Seraphina, 8, and Samuel, 4 -- with his estranged wife, Jennifer Garner.

Watching his brother's win no doubt brought back memories of Ben's first Oscar win with Matt Damon in 1998 for writing Good Will Hunting. In his emotional acceptance speech, Ben thanked Casey, which gave him a chance to give his brother a hard time about omitting him from his speech on Sunday.

WATCH: Ben Affleck Teases He Was 'a Little Taken Aback' That Brother Casey Didn't Thank Him in Golden Globes Speech

"I was a little taken aback," Ben teased during his Jimmy Kimmel Live! appearance on Monday. "That's not the kind of thing I would do. If it's me, I thank people."

Live by Night opens Jan. 13.