Jimmy Fallon Crashes Jonas Brothers Concert for Karaoke Killers and Social Media Is So Confused

"The Tonight Show" host was an unexpected surprise for the crowd at the second stop of the boys' world tour that kicked off August 12 and is expected to continue until June 20, 2024 in Belfast, Northern Ireland.

Fallon shared his big moment with a video posted to his X (née Twitter) account, thanking the band for his "surprise guest spot" and Yankee Stadium for "turning it into the world’s biggest karaoke party. This is one of those nights I will never forget."

That's right, Fallon turned it into a karaoke party during intermission. He came out technically to reintroduce the band for the second half of their show.

But as he proudly strutted onto the stage and announced he "brought my boom box," it was clear he wasn't going to just announced the group. Instead, he decided to do a little hype work, too.

"Are we having fun yet?" he shouted to the enthusiastic crowd. We're not sure anyone in attendance could match his own enthusiasm, though, as he began to jump around while leading them in a rousing rendition of The Killers' "Mr. Brightside."

As for Jonas Brothers, this tour is a culmination of their careers to date, with music from across five different albums represented.

"It’s our most ambitious show we’ve ever put on, in the sense that building out five albums in one night was a challenge that I don’t think we fully understood after we’d already put it on sale," Nick told People of their 67-song setlist.

Tracks come from the albums Jonas Brothers (2007), A Little Bit Longer (2008), Lines, Vines and Trying (2009), Happiness Begins (2019), and The Album (2023), as well as a few standalone singles like "What a Man Gotta Do," Nick Jonas' "Jealous" and DNCE's "Cake by the Ocean."

Fans took to social media to share their videos and express equal parts delight and confusion at Fallon's appearance. It's not just that he dropped in as a special guest, but then leading the crowd in singing a Killers' song at a JoBros show? Yeah, it was kind of random.