"Wow, you look healthy," Kimmel said sarcastically when Affleck, wearing a dramatically oversized trenchcoat, sat down for his chat.
"No offense. I really don't mean to put you in an uncomfortable situation but you look -- you've really ballooned up," Kimmel said in response.
"Thanks, I didn't think this was about body-shaming tonight," the 43-year-old actor said.
"I just think it's gone on long enough," Affleck said of Kimmel and Damon's beef. "I think it's maybe time to bury the hatchet, man!"
"You get to decide when it's time to bury the hatchet?! Do you know what he's done to me?" Kimmel tried to reason, while Damon -- poor guy -- remained kneeling on the floor until Affleck invites him to sit on the couch.
"Wow!" Damon exclaims, as if his life has turned a page: "This feels amazing!"
"I still feel like Dorothy!" an ecstatic Damon says, before Kimmel has the cameraman cut the Oscar-nominated actor out of frame and physically removes him offstage.
After Kimmel showed a photo of the two at the 1998 Academy Awards, the first time they won their Oscar for Good Will Hunting, Affleck made a joke at Damon's expense.
"I've been figuratively carrying him for years! Literally," he jokes.
Earlier in the episode, Damon stealthily trolled an interview Kimmel's sidekick Guillermo was conducting with Sacha Baron Cohen and even popped up in a hilarious Batman v Superman/The Martian spoof.