"I put him on a diet and doesn't he look better for it?" giggles the 38-year-old about her ex-fiance.
"You know what Simon's like, he's so arrogant and he thinks he's so gorgeous - but I was like, `Look darling, even you have put on a few pounds so sort yourself out!'.
"He does look better and now he'll phone me if I'm watching American Idol and say, `Do I look good? Do I look fat?' - and I'm always brutally honest, just like he is!" she laughs, flashing her trademark bright white smile.
The singer teamed up with her ex-manager again for the notoriously fraught X Factor auditions.
And she's adamant that his `Mr Nasty' persona is not an act - and that's exactly why they are still the very best of friends.
"Simon is absolutely being himself, and that is really, really what he's like, which is why our relationship is the way it is - I like that about him because I've always known where I've stood," she explains.
"I mean yes, sometimes he's just mean to be horrible, sometimes he's overtired or in a bad mood, but often it's just that he's never been good at putting his opinion over in a subtle way and he just says it how he feels it.
"Sometimes people do want to slap him for what he says," she adds, "and in the old days I used to!"
When news of Cowell's acerbic style first hit the American airwaves people were absolutely outraged, she reveals.
"He had to have a huge bodyguard and everything - but now you walk down the street with him and people love him. I mean, Oprah Winfrey, my personal hero, recently had an actual Simon Cowell day on the her show - it's just amazing," she grins.
"He's a lot of fun - well, he's been telling the same jokes for the last 20 years and I still laugh so I think that's a pretty good pairing!"
Now living just around the corner from each other in west London, the pair are still so close that it was Simon who gave his best friend away at her 2002 wedding to businessman Andrew Willner.
"I actually met Andrew about 10 years ago and we became really good friends - I even tried to set him up with a couple of my girlfriends who thought he was quite cute but then I ended up with him myself, which was quite nice," she remembers fondly.
She's not turned her back on performing though - Sinitta will be back with her signature song So Macho on ITV1's new talent show Hit Me Baby One More Time, on Saturday April 23.
The show sees vintage stars, including Belinda Carlisle, Carol Decker, Chesney Hawkes and Tiffany, performing their greatest hit and a contemporary song - Sinitta has chosen Single by her friend Natasha Bedingfield. Out of each week's contestants, a public vote decides who goes through to the grand final.
Her long-awaited autobiography is now finished, and she's also keeping her fingers crossed for a role in new movie Ladies Night, directed by Monster's Ball producer Lee Daniels
"When I first went into showbusiness I really wanted to be in a musical and I used to love Fame and Flashdance - this really would just be a dream come true," she beams.
But now she's settled down to family life, her second taste of fame will be very different.
Sinitta admits that after her big break in 1986, she allowed her meteoric success go to her head a little, chalking up romantic trysts with Brad Pitt - not to mention David Essex and John Fashanu - in the process.
"I used to have such tumultuous, crazy relationships when I was younger and I think I was a bit of a wild child to be honest - Andrew is just a really down-to-earth, normal intelligent guy," she smiles.
But it's not just her husband who contributes to Sinitta's new status as a blissfully married wife - she now has two step-children from Andrew's previous marriage, Rudi, 14, and 10-year-old Tamara.
"I have to say, that was a quick learning curve - one day you say `I do' and the next weekend your kids arrive!" she laughs.
"But I've been really blessed in that department because they are so sweet and loving - I wouldn't have been able to have done a better job of it if I'd have bought them up myself."
And she confesses that she and Andrew are trying to conceive themselves - sadly with no luck so far.
"I'm really trying hard but I've had a few complications because I've had fibroids and this, that and the other so now I'm on the road to considering surrogacy or adoption.
"I definitely, definitely want to have my own baby to keep all week long. People say I have the best of both worlds but I really do want my own baby and to see what our baby would look like.
"Andrew is really supporting me in whatever action we can take to make it happen, so fingers crossed. I don't know what to expect but I just think, `Keep your eye on the target' - whatever it takes," she says resolutely, managing to sound as positive and upbeat as ever.
After becoming a born-again Christian in 1994, and eventually a pastor of her local gospel church - Hillsong in London's Regent's Park - Sinitta's rock-solid faith should serve as a source of help and comfort during the testing times to come.
Her return to religion came as much of a surprise to her, she admits. "I wasn't planning it. I went into this church after seeing a picture of a dying child - I know we've all seen them before but this particular one really impacted me.
"I wandered in to Hillsong Church and ended up joining this small group of maybe 20 people - that was 11 years ago and now there are about 4,500 as members," she smiles warmly, adding that the Bedingfield siblings, Natasha and Daniel, have sung with her at Hillsong every Sunday for around six years.
They're not the only talent she surrounds herself with these days. Her main focus, she explains, is spotting new singers.
"That's what I've been doing for the last few years - working behind the scenes, finding and developing new talent."
And yes, she smiles, she's had a hand from Mr Nasty, who's passed on some of his wisdom - although not, fortunately, his people skills.
The third episode of Hit Me Baby One More Time is on ITV1 on Saturday April 23.
Name: Sinitta Renet Malone
Date of birth: October 19, 1966
Significant other: Husband Andrew Willner
Career high: Getting signed to perform Stock, Aitken and Waterman's 80s disco classics So Macho and Toy Boy
Career low: Her single Supreme EP failed to make it into the top 40 when released in 1993
Famous for: Singing So Macho - and dating Simon Cowell
Words of wisdom: On Brad Pitt: "He had such a gorgeous body that women would just grab him and pinch his bum."
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Naz, Windermere (08/05/2005 at 22:23)
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