United Kingdom, March 30 -- AJ McLean and Nick Carter once had a fistfight in front of a naked Kevin Richardson.

The 47-year-old singer revealed that he and Backstreet Boys co-star Nick, 45, got into an altercation over a comic book in front of their bandmate Kevin, 53, who had been trying to break things up when his towel fell down.

Speaking live on stage at a 'Music of the 90s' event as moderated by PEOPLE magazine, he said: "Nick and I have actually been the only ones ever [to have a fistfight].

"He was a big comic book collector, and I went through a really bad acne phase when I was a teenager. I was 14 or 15, and he kept calling me pizza face. And he had just picked up an 'Alien vs. Predator' number one.

"I was like, 'Call me piz...