Simon was joined on the red carpet by his girlfriend Lauren, who gave birth to their son Eric last month, and they certainly gave photographers something to look at!
I Can't Sing, co-written by comedian Harry Hill, is based on The X Factor so, unsurprisingly, Simon was joined by all his cronies at the London Palladium for the glitzy launch night.
His fellow Britain's Got Talent judge Amanda Holden was there, along with Louis Walsh an ex-girlfriends Terri Seymour and Sinitta.
As usual, it was Sinitta who caused the loudest whispers, after she turned up in a bright red dress and jacket with HUGE collar...
Simon was clearly pleased with how the evening went, telling fans on Twitter: "Tonight was a special night. The I Can't Sing opening night was fantastic. Credit to the cast who were on top form."
Sinitta also gushed: "Saw I Can't Sing Musical. ALL the performances are genius! Harry Hill I love you!-insulting+funny Comedy imitating Life!"
We're guessing she liked it then...
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