UPDATE: 5ive have since rebuttled against 98 Degrees, with member Abz Love telling TMZ that he and "[other 5ive member] J were talking about who in the hell gets their band name tattooed on themselves and concluded they must all be jockstraps!” and saying the band "sucked ass and probably still do." (Watch the video below.)

Nick Lachey, throwin' some '90s boy band shade! When the 98 Degrees singer appeared on 'Watch What Happens Live' on Monday, March 17, he was asked a pretty daring question: Which '90s boy band did he think was the lamest? And rather than skirt the question, Lachey answered it outright.

When host Andy Cohen suggested the British group 5ive, Lachey was in total agreement.

"We had a big time beef with those guys," he revealed. "[In 1998], we were on the Smash Hits tour in the U.K. with a bunch of pop groups at the time, and 5ive for whatever reason just had it out for us. We used to battle every night."

Say what? We knew that there was the 'N Sync vs. Backstreet Boys debate, but who knew there had been so much boy band rivalry between 98 Degrees and 5ive?

"It's so funny you called them out," Lachey continued. "That's exactly who I was gonna say!"

It's a good thing 98 Degrees haven't had trouble with other boy bands -- that would've made last summer's Package Tour (with NKOTBSB and Boyz II Men) pretty freaking awkward!

PopCrushers, do you agree with Nick's choice for lamest '90s boy band?

Watch Abz Love of 5ive's Reaction to Nick Lachey's Comments: