The King is “doing fine” but “won’t slow down and won’t do what he’s told”, the Queen has said.
The royal was speaking to novelist Lee Child, who appeared at the second annual Queen’s Reading Room Festival at Hampton Court Palace in Surrey on Saturday.
The author of the Jack Reacher crime thriller series said it “sounds to me like a typical husband”.
The King has recently returned to public-facing duties while still undergoing treatment for an undisclosed form of cancer.
It was discovered during an unrelated procedure for an enlarged prostate, but it is not prostate cancer, Buckingham Palace has said.
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Meanwhile, British-Australian actress Miriam Margolyes said she was “chuffed to buggery” to be at the festival.
She also called it an “incredible honour” and said she had told the Queen she was “very fond” of the monarch.
The Queen spoke to a number of authors at the festival, including Sir Ian Rankin and Ann Cleeves.
The King’s attendance at a D-Day event in Portsmouth on Wednesday involved his first public speech and was his most high-profile appearance since his cancer diagnosis.
On Thursday he made his first overseas trip since being diagnosed to attend commemorations in Normandy.
He is expected to take part in the upcoming Trooping the Colour ceremony, but it is understood he will inspect the soldiers from a carriage rather than on horseback as he did last year.