The music mogul's ex-girlfriend posted a series of tweets saying she will tell the true story of the termination via her Twitter account, asking followers to "retweet" her posts in which she denied claims the abortion was four years ago.
She wrote: "Last weekend a few of the newspapers reported that I had terminated @simoncowell child, some said in 2009, another said behind his back RT.
"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 @janemooresun, don't worry about my ability to remember correctly,its something I'll never forget. (sic)"
In the unexpected series of tweets, Sinitta went on to admit saying it so publicly will be "undignified" - adding she wanted to "sleep on" it before making her revelation - but noted it was something she has to do.
UNJUST AND UNTRUE CLAIMS
She continued: "I know how undignified this is and it sickens me too but I have been dignified throughout so many unjusts 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,im going to set a few things straight even though I am afraid of the consequences.
"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 its important to me. (sic)"
Since the pair split, Sinitta has adopted two children and Simon's girlfriend Lauren Silverman is pregnant with his first son.