The Queen missed Friday night's Royal Variety Performance due to her recent chest infection, according to Buckingham Palace.
In a statement before the event, it said Queen Camilla "continues to experience some lingering post-viral symptoms" and doctors had advised her to rest.
"With great regret, she has therefore withdrawn from attendance at tonight's Royal Variety Performance. His Majesty will attend as planned," the Palace said.
It is the latest event Camilla has missed due to illness, having also had to skip Remembrance events.
She did not attend the Royal British Legion Festival of Remembrance, nor the Remembrance Day service at the Cenotaph, instead marking the occasion "privately at home".
However, last week she attended some public duties for the first time since her illness, hosting a Booker Prize reception at Clarence House.
The 77-year-old told author Percival Everett: "I think I'm on the mend, but these things always take a bit of time to get rid of."
"You think you've got rid of it, then they just sort of hang on for a little bit, but hopefully I'm on the mend now," she added.
The Queen also turned out on Thursday at Buckingham Palace for a reception for winners of an essay competition.
This year's Royal Variety Performance - held at the Royal Albert Hall - was hosted by comedian Alan Carr and actress Amanda Holden.
The line-up included Britain's Got Talent winner Sydnie Christmas and Eurovision winner Nemo.
Singer Sophie Ellis-Bextor and magician Stephen Mulhern also performed.
The King was seen laughing with Sir Elton John on his way into the show and later appeared amused by comedian Matt Forde's on-stage impression of Donald Trump.
Forde mimicked Mr Trump's voice, saying: "They're eating the cats, they're eating the dogs!" - a reference to his much-derided claim about immigrants during a TV debate.
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He then turned to address the King, 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 from the royal box.
(c) Sky News 2024: Queen Camilla misses Royal Variety Performance due to 'lingering' symptoms from chest infection
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