Jimmy Fallon performs his new Christmas song with Meghan Trainor on... 'Jimmy Kimmel Live!'?

Jimmy Fallon stopped by Jimmy Kimmel Live! on Monday to perform his new holiday song, “Wrap Me Up,” alongside music star Meghan Trainor, and seeing the late-night rivals together on the same show was a nice surprise for viewers, and even Kimmel himself.

Fallon broke the news of the song just a couple weeks ago on his program — The Tonight Show Starring Jimmy Fallon — and the track has already become the No. 1 holiday song in the country according to Kimmel. Monday marked the first public performance of the song for Fallon and Trainor.

Here’s a look at how the night — and song — played out.

The cold open

The episode began with Kimmel in his dressing room when Fallon walked in with his guitar. The pair embraced — all the late-night hosts did a podcast together during the writers’ strike — and got to chatting, with Fallon saying that he walked right in the building because security thought he was Kimmel.

Then Fallon asked if he and Trainor could perform their new song on Kimmel’s show. And while the host was happy to oblige, he did ask the obvious question: Why not perform it on Fallon’s own show?

“Thought never occurred to me,” Fallon replied.

The song

When Fallon first announced the song — claiming he loves the holidays — he said that he had an idea for a song about wrapping gifts and sent it to Trainor, who he said he’s “always wanted to do something with.”

Fallon said that Trainor eventually got back to him and had changed the title and some words to the song, taking it from Fallon’s original title “Wrap It Up” to the current title of “Wrap Me Up.”

The song comes after a couple of other Christmas songs that Fallon has released, including 2021’s “It Was A … (Masked Christmas)” featuring Ariana Grande and Megan Thee Stallion and an a cappella cover of “Wonderful Christmastime” in 2017 with the Roots, Paul McCartney and the cast of Sing.

The sign off

After the performance, the show returned with Kimmel on stage with Fallon and Trainor to sign off, and it was Fallon who jumped in and stole one of Kimmel’s signature lines.

“I want to apologize to Matt Damon, I’m sorry I had to do a song,” Fallon quickly said.

To fuel a years-long fake beef with the actor, Kimmel usually says that he ran out of time to have Damon on his show at the very end. Something Fallon apparently wanted to try for himself.

Kimmel went on to praise the pair’s new song and said that he thinks “Mariah Carey is in a lot of trouble,” referencing her long-running holiday hit, “All I Want For Christmas Is You,” consistently being atop the holiday charts.

“Look out, you’re going down Mariah,” Kimmel said.

The viewer reactions

Seeing Fallon on Kimmel’s show came as a bit of a surprise to some viewers, who took to social media with their reactions.

But in the end, as viewers saw recently with John Oliver appearing on The Tonight Show, the late-night hosts have grown closer than ever and aren’t worried about their network’s ratings battles.

Plus, Fallon’s show was a rerun on Monday.

Jimmy Kimmel Live! airs weeknights at 11:35 p.m. on ABC.