The 53-year-old singer was snubbed in favour of Cheryl as guest mentor in Simon's Judges Houses round, and Sinitta is less than impressed with the music mogul's decision, accusing him of performing a U-turn on past promises.
She said: ''I will always love Simon. He is like a father figure meets brother figure and ex-lover figure to me, and of course my mentor for over three decades.
''But right now he can kiss my black ass.''
Sinitta claimed Simon previously offered her a the job for life and the singer was hugely excited about appearing on the show, having been forced to pull out last year due to a breast cancer scare.
Speaking to The Sun newspaper, she explained: ''Simon promised me the job for life and said he didn't ever want to do it with anyone else.
''Last year I had a breast cancer scare and was having a biopsy done so I missed it and this year I was excited to be clear, healthy and fearless and they did this.''
Sinitta admitted, too, that her frustration was exacerbated by her painful split from her long-term partner Jason Gale.
She said: ''I am single and wanted to work to get through this phase. Jason and I are still friends and care for each other but broke up in January. It's a crazy time.''
Despite her recent setbacks, Sinitta has pledged to refocus and keeping working towards her other ambitions.
She shared: ''I have sulked and pouted and had the diva tantrum after my time, money and plans were wasted.
''My anger wants to slap all their butts and demand an apology and compensation. But they have no class so if they think they can do it and get away with it, a massive sensitivity chip is missing.
''I am a fighter, I will get another role and be fabulous.''
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