Simon Cowell said attending the world premiere of Harry Hill's X Factor spoof musical I Can't Sing! was like seeing his second baby born this year.
The music mogul - who last month became a father for the first time - is one of the show's financial backers, and his recent parenthood is reflected in its script.
Simon, who walked the red carpet at the Palladium in London with girlfriend Lauren Silverman, said: "It's like my second baby this year, it feels like that.
"It's exciting, and I never thought I'd be in this spot. I don't know much about the West End or musicals but the very first time I saw the run through I really, really liked the show.
"And now I've seen the Twitter reaction to the previews and the people who've seen it really love it. So I'm thrilled."
The production, which stars Nigel Harman as a Simon-like show boss, takes an affectionate swipe at a number of figures associated with the ITV show with characters based on Cheryl Cole - who is to return to the singing contest later this year - and Louis Walsh. Take That star Gary Barlow gets a nod with a dog named after him.
Simon admitted: "It's embarrassing, but I've got a thick skin."
Other celebrity guests at the opening night included Louis Walsh, Sinitta, former X Factor stars Rylan Clark and Stacey Solomon and Britain's Got Talent judge Amanda Holden.
There have been some teething troubles with the show during the early days of its preview run at the theatre, with scheduled performances put back by a few days in order to sort out issues with the way it is staged.
And guests at the first preview reported that too was hit by a 50-minute interval, although producers are now understood to have got the delays under control as the show has bedded in.
But Simon said: "It's a big production, that's why you have all the previews and you work everything out. But it worked out fine in the end."
Harry Hill said he was confident about opening night, insisting: "I feel excited more than nervous."
"We've run it now for four weeks and it's always gone really well, so, the law of averages..."
And he also promised he hadn't held back when mocking Simon or any of the other judges. Harry said: "We never thought twice about it. We wrote what we wanted to write and he was always fine about. I'm not the sort of person who is nasty for the sake of being nasty."
Simon later spoke of how much he had enjoyed the evening, saying 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. Check out the reviews."