In a public show of togetherness, the couple kissed in front of the cameras as they arrived at the London Palladium for the launch of the West End show, a spoof of The X Factor.
Just six weeks after giving birth to son Eric, Lauren, 36, looked sensational in a fitted black dress. Her partner clearly agreed, and kept the American socialite close by his side all evening as they mingled at the star-studded event.
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Lauren and Simon looked loved up
The musical tells the story of a girl called Chenice who auditions for the show. Nigel Harman stars as X Factor supremo Simon, and other characters have been based on the likes of Louis Walsh and Cheryl Cole.
Writer Harry Hill said the show was an "affectionate spoof, and occasionally we go for the jugular".
There's no bad blood between Simon and Harry Hill who wrote the spoof musical
Among the famous faces in the audience for the opening night was Amanda Holden, who hit all the right notes with her outfit; white Zara shorts, a Victoria Beckham blazer and a lacy top.
Nick Candy, Kate Beckinsale and David Walliams turned up to show their support
Sinitta stood out in a dramatic plunging red gown, while Mezghan Hussainy – another of Simon's exes – wowed in a see-through lace top teamed with a figure-hugging skirt.
Bringing Hollywood glamour to the opening was Kate Beckinsale, who tried to make a low-key arrival at the theatre. She did spend time catching up with David Walliams and Nick Candy before heading inside to watch the show.