Jimmy Fallon Turns Jonas Brothers Concert Into Massive Karaoke Party

Fans attending night two of the Jonas Brothers The Tour stop in New York City over the weekend were treated with a surprise before the band even stepped foot on stage when Jimmy Fallon was introduced as the night's surprise guest and led the sold-out crowd in a massive singalong.

The late-night talk show host took the stage at Yankee Stadium on Sunday (August 13) as the surprise guest ahead of the JoBros performance, and he turned the crowd into the "world's biggest karaoke party" when he led them in an enthusiastic rendition of The Killers' mega-hit "Mr. Brightside," jumping around the stage and hyping up the crowd as everyone belted along to the chorus.

Fallon took to Twitter Sunday night to share video of the night he will "never forget."

"Huge thanks to [Jonas Brothers] for giving me the surprise guest spot on 'The Tour' tour," he said before going on to praise all the fans in attendance for their enthusiasm. "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."

Fallon followed up his initial post by also giving a shoutout to The Killers for "writing a JAM."

The Jonas Brothers kicked off The Tour on Saturday (August 12) with a show that includes music from their entire discography. When previewing what fans could expect, they shared that they were going to perform one of their older songs for the very first time.