The King says he has been “reduced to tears” by the “many wonderful messages and cards” he has received since his cancer diagnosis.
The monarch, 75, was speaking with Rishi Sunak in his first face-to-face audience with the PM since Buckingham Palace announced he had a “form of cancer”.
“I’ve had so many wonderful messages and cards, it has reduced me to tears most of the time,” the king told Mr Sunak.
The prime minister said it was “very nice to see you”, prompting the King to joke: “A bit of a gap… I’m afraid.”
“I hear there has been a lot more potential attention on those main, wonderful cancer charities, many of which I have been a patron of for years,” he added.
Mr Sunak replied: “They do a lot of wonderful work.”
The King had been staying at Sandringham, in Norfolk, following his first round of cancer treatment in London last week.
Royal correspondent
The fact the King allowed a camera in, albeit briefly, is highly unusual, but of course these are unusual times. What did we see?
Well the King seemed in good spirits, cheerfully greeting Rishi Sunak, and we had an insight into how moved he’s been by the cards and messages of support.
The decision to show us this audience is significant. The King knows, like his late mother once famously said, he has to be seen to be believed. The trouble is his cancer diagnosis means that’s possible.
He’s been advised not to carry out public duties, but as we’ve been told, he is continuing with his state business – which includes his weekly audience.
What goes on between monarch and Prime Minister normally stays inside palace walls. But in another gesture of openness, similar to the King’s decision to share his cancer diagnosis, part of this private meeting was made public.
There is however a danger. These photo opportunities will be subject to intense and possibly intrusive scrutiny. Remember there’s not actually much we’ve been told about the King’s cancer.
We don’t know what the diagnosis is, or what kind of treatment he’s receiving. For now, the image the palace wants us to see is business as usual.
Although most would agree, it’s currently anything but.
On Sunday, the King was spotted smiling and waving to onlookers before attending a service at St Mary Magdalene Church.
Buckingham Palace announced earlier this month that the King had been diagnosed with a form of cancer while undergoing a procedure for an enlarged prostate.
The palace did not release details about the type of cancer or the type of treatment.
Earlier this month, at an event at Salisbury Cathedral, the Queen spoke about her husband’s diagnosis for the first time.
She told Ben Abbott, a critical care paramedic: “He is doing extremely well under the circumstances. He is very touched by all of the letters and messages the public have been sending from everywhere. That’s very cheering.”
The announcement was followed by a rare return to the UK for the King’s youngest son, Prince Harry, who flew over from the US and visited his father.
Meanwhile, Prince William, who has been assisting the King with royal duties, spoke for the first time since his father’s cancer diagnosis earlier this month.
“We really appreciate everyone’s kind messages, thank you,” he said, as he arrived at a gala for the London Air Ambulance Service in central London on 8 February.
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The King’s treatment as an outpatient started earlier this month.
Buckingham Palace said the King had postponed all public-facing duties following his cancer diagnosis, but that he planned to continue with work on his red boxes of state papers.
The palace also said that the King planned to switch his weekly audience with the prime minister from face-to-face to over the phone for two weeks.
