Mel B threw a cup of water over Simon Cowell when her fellow talent show judge made a joke about her wedding night.
The former Spice Girl, 42, is divorcing Stephen Belafonte.
Asked by America’s Got Talent host Tyra Banks how an act on the show made him feel, straight-talking Cowell replied: “I’m imagining this would be like Mel B’s wedding night, a lot of anticipation, not much promise or delivery.”
His comments shocked the studio audience and surprised Brown, who despite smiling, threw a cup of water over Cowell, 57.
Cowell, left wearing a water-splattered, open neck shirt, smiled back as Brown walked off set for a short time.
Banks commented: “Mel B is out.. this is live TV y’all.”
An America’s Got Talent employee suggested the incident had been spontaneous, writing on Twitter, “that was not planned”.
Cowell’s TV shows have a history of judges throwing water over each other – most memorably with Sharon Osbourne drenching Louis Walsh on The X Factor.
Brown married Belafonte in Las Vegas in June 2007. She filed for divorce on March 20, citing “irreconcilable differences”.
A full divorce hearing is scheduled to begin on September 25.