ET was exclusively with boy band New Kids on the Block at the rehearsal for the last night of their tour at Radio City Music Hall in New York City when a surprise group of guys joined them for a special surprise performance.

None other than the Backstreet Boys joined the NKOTB to sing BSB's hit song "I Want it That Way." "I think this is definitely a special collaboration and timing is everything in show business," New Kid Joey McIntyre told ET.

Backstreet Boy Howie Dorough adds, "We've always said they've inspired us to be the group that we are." New Kid Donnie Wahlberg jokes of the groups' fan bases, saying, "They have very loyal fans and we have very loyal fans, but I think looking at the few women who were sprinkled around during rehearsal, there was just a look that I haven't seen too often."

Nick Carter of BSB says of the surprise show, "I think people are going to explode."