The King has carried out his first in-person engagements since his cancer diagnosis was confirmed earlier this month.
Charles, 75, returned to Buckingham Palace in London on Wednesday to hold an in-person Privy Council before his traditional audience with Prime Minister Rishi Sunak.
For the past two weeks, the King and the Prime Minister have conducted their weekly meeting by telephone while Charles is residing at Sandringham in Norfolk.
It was always understood that the weekly audiences would resume on 21 February, after the King's cancer diagnosis was made public on 5 February.
© PA ImagesAt Prime Minister's Questions earlier this month, Mr Sunak said: "I know the thoughts of the House and the country are with the King and his family. We wish His Majesty a speedy recovery and look forward to him resuming his public-facing duties in due course."
After their meeting on Wednesday, Buckingham Palace released a rare video of their tete-a-tete.
“Wonderful to see you looking so well,” said Mr Sunak. “It’s all done by mirrors,” the King replied, laughing.
“We’re all behind you,” said the Prime Minister. “The country is behind you.” To which an emotional King Charles responded: “I’ve had so many wonderful messages and cards. It’s reduced me to tears most of time.”
The monarch holds a private weekly audience with the Prime Minister to discuss Government matters.
© PA ImagesThough the King is meant to remain politically neutral on all matters, he is able to "advise and warn" his ministers – including Mr Sunak – when necessary.
Charles has postponed all public-facing duties, but is continuing with behind-the-scenes work on his red boxes of state papers.
He is set to miss a Thanksgiving Service for his close friend and second cousin King Constantine II of Greece as he continues his treatment for cancer. Queen Camilla will lead the royal family at the memorial at St George's Chapel in Windsor on Tuesday 27 February.
Constantine, the last king of Greece, died at the age of 82 in January last year.
Charles was unable to attend Constantine's funeral in Athens last year due to commitments including meeting the president of Cyprus, and his sister the Princess Royal represented him at the ceremony.
Buckingham Palace announced that a "form of cancer" had been found while the King was being treated in hospital for an enlarged prostate last month.
The full statement released on 5 February read: "During The King's recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted. Subsequent diagnostic tests have identified a form of cancer.
"His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties. Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual.
© Getty"The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure. He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible.
"His Majesty has chosen to share his diagnosis to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer."
