The monarch was filmed shaking hands with British Prime Minister Rishi Sunak as he arrived at Buckingham Palace on Wednesday afternoon.
Their meeting marked the resumption of their weekly encounters to discuss government matters.
Though the King has stopped carrying out public engagements while he undergoes his cancer treatment, he is continuing with his duties as head of state.
Images from the British news agency PA Media show Charles, dressed in a suit and tie, greeting Sunak with a broad smile and the pair exchanging pleasantries.
“We’re all behind you. The country is all behind you,” Sunak said, according to PA Media.
Charles replied: “I’ve had so many wonderful messages and cards. It’s reduced me to tears most of the time.”
They went on to discuss how the King’s illness had shone a spotlight on cancer charities, with the King describing such organizations as “wonderful.”
Prior to his meeting with the prime minister, Charles held an in-person Privy Council at the royal residence, which was attended by ministers including Lord President of the Council Penny Mordaunt.
On February 6, Buckingham Palace announced Charles, 75, had been diagnosed with an undisclosed form of cancer and would be stepping back from public-facing duties while he undergoes treatment.
It was identified after he was admitted to a London hospital for a corrective procedure for an enlarged prostate last month, the palace said. Prostate cancer has been ruled out to CNN by a royal source, who did not provide any further detail.
Charles is expected to carry on getting his daily red boxes with government papers so he can continue working through state documents at home. CNN understands it is anticipated the King will continue his weekly audience with the prime minister and alternative arrangements will be made if his doctors advise him to minimize in-person contact.
Prince William, Charles’ son and the heir to the throne, and Queen Camilla are expected to take on more public engagements to account for Charles’ absence.
Charles’ first public outing since the diagnosis was to attend a church service alongside Queen Camilla at St Mary Magdalene’s church on the monarch’s Sandringham estate in eastern England on February 11.
He has previously expressed gratitude to the public for their support, saying it brought him “the greatest comfort and encouragement.”
This is a developing story and will be updated
