In a surprise announcement on their Web site Thursday afternoon, the brothers – Kevin, 21, Joe, 19, and Nick, 16 – were to perform a free concert that very night at New York's Irving Plaza for the first 700 fans who lined up at the door.
The band performed songs from their old albums as well as a few new tunes from their upcoming fourth album, Lines, Vines and Trying Times, which drops June 16.
Fans were ecstatic about the band, singing along to old hits and rocking out to new ones. By the end of the concert, the brothers had stripped down to white v-neck undershirts as approving fans squealed with excitement.
Nick, who has recently been spotted spending time with ex-girlfriend Miley Cyrus, 16, on Georgia's Tybee Island where she is filming The Last Song, kept mum throughout the concert about their friendship and didn't perform their recent duet, "Before the Storm."
He did, however, get personal with the crowd, saying, "It's never the end, it's a new chapter. This is how it worked in my life."
Reps declined to comment on whether the two are dating again.
Reporting by SHARON COTLIAR and MICHELLE TAN
Rob Hoffman / JBE / Getty