Tweeting on Friday night that she needed to "set a few things straight", the So Macho singer claimed she had been prevented from "defending" herself, but did not deny the reports.
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"Last weekend a few of the newspapers reported that I had terminated @simoncowell child, some said in 2009, another said behind his back," she wrote.
"They stopped me defending myself in paper where started, so now I have to tell the whole truth of the @SimonCowell baby termination here.
"Firstly the baby termination wasn't in 2009," she said, before naming a journalist on Twitter and adding, "Don't worry about my ability to remember correctly, its something I'll never forget."
She went on: "I know how undignified this is and it sickens me too, but I have been dignified throughout so many unjust and untrue claims and accusations...
"I don't want to hurt the people I have loved, but I don't want to always be the one who gets hurt either… Today I snapped, enough is enough… this isn't the best place (practically) as SO much to say. I'm going to set a few things straight even though I am afraid of the consequence.
"I need to pray on this, I need to sleep on this, but I know somehow I need to do this. I'm sorry but it's important to me.
"I'm sorry, this is so hard. Lots at stake, needs to be said, but said properly… Excuse me for coming 'undone' on here."
Then, on Sunday, in a bizarre twist, Sinitta, who has two adopted children, appealed to ITV talk show host Jeremy Kyle in her quest to set the record straight.
Determined to tell the world her version of events, she again took to Twitter to ask Jeremy if she could appear on his famous talk show — and even offered to take a lie detector test live on air.
"Jeremy Kyle, I know I declined your celebrity chat, but I'd love to do your show PROVIDED you provide a lie detection device… #thisHAStoend," she tweeted.
"A 'testimony' is when you tell your story 'warts and all' in church or to a group of people, to show your journey from 'lost to found'..."
So far there has been no comment from Simon, who is famously expecting a baby with New York socialite Lauren Silverman.
Sinitta was 19 when she first met the multimillionaire media mogul, and he promised to make her a star. They began an on-off romance which turned into a strong and enduring friendship, with the result that Sinitta has been a permanent fixture in the music mogul's life ever since the 80s.
In an exclusive interview with HELLO!, she admitted she had struggled to accept the news that Simon is starting a family with another woman. Last week, a source told the Daily Star:
"The news has knocked her completely and she hasn't been in a good way since she found out. Simon always told her he didn't want children.
"She didn't think he would ever start a family and believed if he ever changed his mind, he would start a family with her. She is finding it hard to control her emotions and friends are worried about her."