Simon Cowell and Mel B reportedly had a huge bust-up after Saturday night's show, after she branded his act Fleur East a cheat.
The 54-year-old head judge is said to be fuming with Mel, 39, for suggesting Fleur, 26, wasn't following the rules by having her backing track turned up.
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Following Fleur's performance of It's A Shame by Monie Love, Mel commented: "I love the rapping, I love the whole look. My only thing is the chorus, I couldn't hear your voice. It was like cheating."
Simon immediately leapt to Fleur's defence, saying: "You're making the audience think this girl is cheating and that's unfair. She's not cheating.
"We put the backing vocals up because she was singing a different thing during the chorus."
But their disagreement apparently continued off-screen, with a source telling the Mirror: "Simon likes a lively panel but Mel took it too far."
What did you make of Mel's comments about Fleur?