The former popstar had an on-off relationship with Cowell for many years and the pair remained close friends, with Sinitta a regular fixture during the Judges' Houses round of The X Factor - including one memorable moment when she appeared wearing just leaves as an outfit.
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But despite their close history, she told The Mirror that she would not be at his upcoming wedding to Lauren Silverman because she will be on tour in the cast of musical Chicago.
And as she made a quip about a themed wedding gift, Sinitta, 58, appeared to give a good idea of what date the private ceremony could be taking place.
She said of her absence from the wedding, rumoured to be taking place in London: "I’ll send him the lucky Irish leaf – I’ll send him a shamrock from Louis (Walsh)."
The singer is due to take up her role of Matron Mama Morton in Chicago at the Grand Opera House in Belfast from June 6 to 11 and then in Plymouth from June 14 to 18, suggesting with her choice of present that Cowell's wedding could be during the earlier June dates.
Sinitta shares the musical role with Sheila Ferguson and Gemma Collins, with the three women performing shows on rotation.
Revealing she'd been to watch Ferguson recently, Sinitta added: "I’m also going to travel to Oxford to see the GC – because I’ve got to see the GC! She’s a reality show diva, and I’d say that I’m a pop diva!"
Cowell has downsized much of his Syco business since the beginning of the year and recently said that he had been looking at Britain's Got Talent acts differently now that he is not trying to sign a new popstar.
Asked by The Sun whether having wound down his record label was changing the way he judged on the ITV talent contest, he said: "I suppose so. I think in the same way as you buy an album or a track, you like what you like."
Watch: Simon Cowell is getting married next month