"I kind of imagine this would be like Mel B's wedding night," Cowell said after an escape artist had a technical malfunction during his performance. "A lot of anticipation, not much promise or delivery."
The "America's Got Talent" official Twitter account shared a gif of Brown's shocked reaction to Cowell's joke.
Brown, who filed for divorce from husband Stephen Belafonte in the spring, spoke to Entertainment Tonight after the incident.
"I told him he was an [expletive] and that was it, and he goes, 'Oh, whatever,'" she added.
Mel B filed for divorce from Belafonte in March after splitting from the film producer in December after nearly 10 years of marriage.
She later obtained a temporary restraining order against Belafonte after alleging he was abusive.