Matt Damon Admits 'It Was Painful' Being Ben Affleck's Friend During J.Lo Romance

'The Martian' star says Affleck is the most 'misunderstood' person in Hollywood.

Matt Damon and Ben Affleck have one of Hollywood's most famous friendships. From winning an Oscar together for writing Good Will Hunting, which they also co-starred in, to co-producing the filmmaking docu-series Project Greenlight, the two have been inseparable for years.

Now, speaking with The Hollywood Reporter while promoting his upcoming film The Martian, Damon opened up about Affleck and the recent personal troubles his friend has been facing.

WATCH: Matt Damon Says Ben Affleck Gay Rumors 'Put Us in a Weird Position'

"There's nobody who's more misunderstood," Damon said of Affleck. "Ten years ago, the public image of him could not have been farther apart from who he actually is."

A decade ago Affleck's career was far different from the one he's been enjoying in recent years. A string of unsuccessful or critically dismissed films had given Affleck a bad name, and relationship drama with his then-fiancee, Jennifer Lopez, kept his name in the headlines for all the wrong reasons.

WATCH: What Ben Affleck and Jennifer Garner's Famous Exes Said About Their Failed Romances

"It was like he was being cast in a role, that he was a talentless kind of meathead, with his whole relationship with Jennifer Lopez. He just got cast as this person that he wasn't," Damon said, adding, "It was just really painful. It was painful to be his friend, because it wasn't fair, you know? To my mind, nobody really got him at all."

However, Damon celebrated his friend's career comeback – including a successful directing career and a slew of popular and acclaimed performances – and credited Affleck's work ethic for his success.

WATCH: Matt Damon Shares Update on Ben Affleck, Admits 'Marriage Is Insane'

"Through his work, he climbed from the bottom of the mountain all the way back up to the top and past where either of us had ever been," Damon said.

Damon stars in Ridley Scott's highly anticipated sci-fi drama The Martian, which hits theaters Oct. 2. Check out the exciting trailer below.