Now RadarOnline.com has exclusively learned that the bad blood has spilled over backstage!
Cowell, a well-placed source tells us, has been intervening in Nicole's team all week in the lead-up to tonight's show which is the first episode where the viewing public votes.
"Simon said last week he didn't like Stacy Frances' song and called her a 'church singer' - which Nicole took as a huge insult," the source says. "It actually wasn't. It was about Nicole picking the wrong style song for Stacy. This week Simon started appearing at Nicole's acts during rehearsals. He thinks it's hilarious that Nicole got so mad with him last week and loves the fact Nicole's acts seek his approval. This week he's even taking credit for choosing Stacy's song"
Cowell admitted today, "Some of the best singers in the world are what I call church singers, like Aretha Franklin - that's what I mean, what's wrong with that? But Stacy got it so wrong last week. So I'm going to take responsibility for what she's singing tonight. If she gets it wrong tonight I'll take full responsibility - but this is more me than Nicole with Stacy this week, its been me guiding her."
He even went on to criticize Nicole's mentoring of LeRoy Bell.
"I don't think Nicole's connected with him. You have to get into a contestants head and I'm not sure she has done that yet."
All of this is going down on the same day Fox announced it is renewing X Factor for another season.