George Clooney didn't have to look far to find someone to help take care of he and wife Amal's 4-month-old twins Ella and Alexander

Not even taking care of George Clooney’s newborn twins could keep Matt Damon from doubling down on his longtime feud with Jimmy Kimmel.

Damon debuted as George and Amal’s “manny” to 4-month-old twins Ella and Alexander on Jimmy Kimmel Live Monday night – but quickly devolved into slinging insults (and eventually even throwing up middle fingers) at the late night host.

“He’s my manny,” Clooney told the audience of his longtime friend and Ocean’s Eleven costar as Damon rolled in pushing a double stroller and carrying a diaper bag on one shoulder and spit-up towel on the other. “He’s just very good with the kids!”

Of course, the bit was a setup for Kimmel from prankmaster Clooney, there to taunt Kimmel with his No. 1 rival.

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Credit: ABC

Matt Damon

“I’m his manny. It’s a nanny who’s a man,” Damon, 47, explained — his experience as a father to four daughters surely coming in handy. “You’re not a man,” Kimmel quipped back, later ripping into Damon’s body. “So I guess by your physique that you’re breastfeeding too?”

“I actually just wanted to get their nap so I brought them to a place where they wouldn’t be woken up by laughter,” Damon shot back.

The hilarious back and forth continued before Clooney asked Damon to show Kimmel and his audience the kids. That’s when Damon delivered the ultimate mic drop, lifting a fake Ella and Alexander out of their strollers and flipping Kimmel his two middle fingers.

“There they are right there,” Damon said. “This is screw, and this is you. Screw you!”

Credit: ABC

Matt Damon, George Clooney and Jimmy Kimmel

Credit: ABC

Matt Damon

WATCH: George Clooney Talks Twins at Suburbicon Premiere with Wife Amal

While Damon might not make the best manny to Clooney’s kids, he is starring in Clooney’s new movie Suburbicon — which the ER alum directed, co-produced and co-wrote alongside his longtime collaborators, the Coen brothers.

And Damon still gets plenty of one-on-one time with Clooney’s kids, who have developed quite differing dispositions.

“They start out with a personality right off the bat,” Clooney told Entertainment Tonight on Sept. 1. “[Alexander] is a thug already. [Matt] saw him. He’s a moose! Literally, he just sits and he eats.”

“He looks like he could bounce right now, some place in Hollywood,” Damon chimed in.

“Like, checking IDs on the way into the nursery,” Clooney continued.

In contrast to Alexander, Clooney said Ella is “very elegant and all eyes.”

“She looks like Amal, thank God,” he joked.