He then wished “everyone a very enjoyable evening” at the performance, which was presented by Amanda Holden and Alan Carr.
The King seemed amused as he laughed at comedian Matt Forde’s impression of Donald Trump. During the show, the comedian referenced claims made by Mr Trump during his presidential debate against Kamala Harris earlier this year that illegal immigrants from Haiti were eating locals’ pets in Springfield, Ohio.
Forde exclaimed in the president-elect’s voice: “They’re eating the cats, they’re eating the dogs!”
He then turned to address the King 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 the royal box.
It is the first time he has attended the event in his position as patron of the Royal Variety Charity, which he accepted earlier this year. The late Queen Elizabeth II also held the role.
“The charity’s crucial work in assisting those who have fallen ill, had an accident or hit hard times is as essential now as it ever has been,” the King said at the time.
“I would like to thank all of those who have worked so hard to stage this year’s production and wish everyone a very enjoyable evening.”