Jimmy Fallon recently surprised fans by performing a song at a Jonas Brothers concert.
The Tonight Show host, 48, surprised concert-goers by walking onstage to sing The Killers’ rock classic “Mr. Brightside” at The Jonas Brothers’ tour stop in New York City on Sunday.
Fans posted videos on Twitter (now known as X) describing how surprised they were to see Fallen at the band’s second sold-out show at Yankee Stadium, where their new dates called The Tour Started on Saturday.
According to one fan’s video “How would you all like to be in the world’s biggest karaoke party for two minutes?” Fallon asked the 60,000 crowd.
“I hope you know the word, it’s ‘Mister’.” Brightside,'” he added before the crowd joined in energetically with his performance.
“I brought my boombox,” Fallon said in another fan video, in which he is seen pointing to a cylinder bag held on stage with a cross-body strap.
“Nick asked him to come do it a week ago,” a source tells PEOPLE about the surprise musical moment. “He told him he could do whatever he wanted and Jimmy Fallon was like, ‘Anything — even karaoke with my boombox?!’ “
The source also confirmed that Fallon performed the song “without any rehearsal”.
“Jimmy Fallon suddenly appeared at Jonas Brothers Yankee Stadium Night 2 and is leading the crowd in “Mr. Brightside,” a fan captioned another video post.”
The Jonas Brothers recently spoke exclusively to PEOPLE about their tour, calling it their “most ambitious show” ever.
Promising to cover their entire history as a band, the trio of brothers – Joe, 33, Nick, 31, and Kevin, 35 – will perform 90 performances in 20 countries.
“If you’re an OG superfan or if you’re more into the new stuff, I think you’re going to be pleasantly surprised and have a great time,” Joe told PEOPLE. “There’s something for everybody.”
Another video shows Jimmy Fallon telling the audience, “I brought my boombox,” pointing to a portable speaker he was wearing as a cross-body bag.
“Huge thanks to the Jonas Brothers for giving me the surprise guest spot on The Tour tour,” Jimmy wrote on Twitter/X after the gig. “And thank you to Yankee Stadium for turning it into the world’s biggest karaoke party. This is one of those nights I will never forget.”
“And thanks to The Killers for writing A Jam,” Jimmy said in a separate post.
“I would pay to go to a karaoke concert with Jimmy Fallon as the headliner,” one fan commented on TikTok.
Another TikTok user wrote, “He was waiting for this moment and he deserves it.”