Charles attended the show at the Royal Albert Hall in London for the first time as patron of the Royal Variety charity, following in the footsteps of his mother, the late Queen Elizabeth II.
The monarch arrived alone on Friday evening after Camilla pulled out of the event at the last minute, having been advised by doctors to rest following her recent chest infection.
Show hosts Alan Carr and Amanda Holden expressed gratitude at Charles' attendance despite his wife's lingering illness, and enthusiasm at the news their comic numbers on stage made the monarch laugh.
"His Majesty was amazingly charming - he said we definitely earned our pound that we got paid. We mentioned Her Majesty and wished her well," Holden said.
"He did so well to be here. He was really funny - I've always said out of everyone he's got the best sense of humour in the whole of the royal family."
Elton John also presented a musical number from his new show and shook hands with King Charles. (AP PHOTO)
Carr, who met Charles for the first time after the event, said the King was "really sweet" as he apologised for the Queen's unexpected absence.
"We also got the goss that he was laughing at some of our bits so we're very happy" he said.
"If you get a laugh, well - that's what you're here for."
Performers included comedians Scott Bennett, Larry Dean, Ellie Taylor and political comic Matt Forde, whose impression of Donald Trump drew an amused reaction from the King.
The performance saw Forde reference the unfounded claims Mr Trump repeated during his presidential debate with Democrat candidate Kamala Harris that illegal immigrants from Haiti were eating pets in the Ohio city of Springfield.
Forde exclaimed in the president-elect's voice: "They're eating the cats, they're eating the dogs!"
He then turned to address Charles from the stage, saying in Mr Trump's voice: "Your Majesty King Charles, you're named after a spaniel - be very careful, they'll eat you alive."
The King was seen laughing in response from the royal box.
The night saw performances by Britain's Got Talent 2024 winner Sydnie Christmas, who sang Imagine Dragons' Believer, Cirque du Soleil acrobats and musical numbers from Cameron Mackintosh's production of Oliver!, starring Jack Philpott in the title role.
Sir Elton John and his husband David Furnish also presented a musical number from their new show The Devil Wears Prada, based on the 2006 Oscar-nominated film, with Vanessa Williams as fearsome fashion magazine editor Miranda Priestly.
Money raised by the show will help people from the world of entertainment in need of care and assistance with the Royal Variety Charity launching an initiative to help those with mental health issues.
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