King Charles pictured laughing as he reads card from well-wisher among 7,000 sent since cancer diagnosis

The King has been overwhelmed by messages of support from around 7,000 well-wishers worldwide since his cancer diagnosis, Buckingham Palace says.

Many people have written to tell him of their own experiences of the disease or offering advice. One person told him: “Chin up, chest out, remain positive and don’t let it get you down. Trust me, it works, but the main thing is family.”

A child wrote: “Never give up. Be brave. Don’t push your limits. Get well soon.”

Charles was particularly taken by a card showing a dog feeling sorry for itself after medical treatment, with the message: “At least you don’t have to wear a cone!”.

The collar, which stops animals aggravating a wound or stitches after an operation, is sometimes called the “cone of shame” by pet owners, or an “Elizabethan” or “E-collar”.

The King laughed when he came across the card, Buckingham Palace’s correspondence team said.

Well-wishers who have included an address will receive a thank you, the team said.

On Wednesday, the King carried out his first face-to-face official duties – an audience with prime minister Rishi Sunak and a privy council meeting – since his condition was made public.

Footage showed Mr Sunak saying, “Wonderful to see you looking so well,” and the King replied: “It’s all done with mirrors.”

The 75-year-old said he had been reduced to tears by the messages and cards of support he had received. The prime minister told him the “country is behind you”.

Since the diagnosis, Charles has postponed all public duties, but is continuing to work on his red boxes of state papers.

Prince Harry made a whirlwind visit to see his father in London, after the King gave him the news of his diagnosis.

The Duke of Sussex spent almost as much time in the air as he did in England, on his first visit to his homeland since September.

The journey from the US took Harry more than 10 hours, but his meeting with King Charles at Clarence House in London reportedly lasted less than an hour.

Harry later said his father’s condition could “reunify” the royal family, fuelling speculation the prince could be allowed back into the fold. He said he was grateful to be able to spend time with his father, and reportedly suggested he would be willing to temporarily return to duties while the King is ill.

The King has been seen smiling and waving while attending church services at his Sandringham estate in Norfolk.

The type of cancer he has has not been revealed; nor is it known how many rounds of treatment are planned, but so far he has had at least two.

Before his appointment with the prime minister, he held a meeting at Buckingham Palace of the privy council, whose attendees included the lord president of the council Penny Mordaunt.

At monthly council gatherings, the King gives his formal approval to orders that ministers have already approved.