Following a series of extraordinary Twitter postings, the 49-year-old singer opened up on the termination which left her and the music mogul completely "devastated".
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"Simon was very concerned and by my side," she told the Sun. "It was upsetting and it was something very difficult that we dealt with together. It's such a heartbreaking thing to go through. It was devastating for both of us."
Echoing her exclusive interview with HELLO!, the former pop star discussed her feelings towards Simon, and her reaction to the news that he is having a baby with Lauren Silverman.
Sinitta and Simon Cowell have been friends for years
"I have always admitted I wanted to marry him and have children with him," she said. "Not just because I love him, but because I thought it would be good for him. I think he thought he didn't want children and he would never want children. And I believed him."
Sinitta, who adopted two children with her ex-husband Andy Willner, Magdalena, eight, and Zac, seven, previously told HELLO! that she was "completely and utterly stunned" when Simon called to tell her the pregnancy news.
"I was in such a daze, to the point where I wondered if I was dreaming," she said. "He sounded… odd, calm, strange, which threw me.
"I don't mind admitting all sorts of emotions were running around inside me. He was very concerned how I would take it, which, on reflection, he didn't need to be. He didn't owe me that consideration."
Sinitta with her two children
"I suppose there has been a certain amount of comfort for me in my not having a child with Simon because he never wanted to have children at all," she added. "That's who he was, so you accepted it.
"Then, to discover that he is going to have a child, only with someone else and they're building this life together… All those crazy things were going through my head and it's not fair and it's not pertinent to Simon and Lauren's situation and I don't have a right to feel that way. But I'm being honest."
The star told the Sun that while it was a "big adjustment" seeing Simon happy with Lauren — especially since she considered the 36-year-old to be "like a sister" — she has sat down with the pregnant socialite to smooth things over.
Sinitta also insisted that while she still loves her former flame, she is no longer in love with him, wishing the parents-to-be every happiness for the next "fascinating" stage of their journey.