Charles, 75, who has been diagnosed with a type of cancer, joined a meeting of the Privy Council at Buckingham Palace – followed by an audience with the Prime Minister.
Palace sources said the double-header was a sign of “State business, as usual” coming over two weeks after his cancer bombshell was announced.
The King’s last in-person outing was an investiture at Windsor Castle on December 19.
Charles today held a Privy Council with Penny Mordaunt, Lord President of the Council and Leader of the House of Commons, Home Office minister James Cleverly, Alister Jack (cor), Secretary of State for Scotland, Gillian Keegan, education minister.
The King and council also swore in new member Michael Tomlinson, Minister of State for Illegal Migration.
After the private 4.30pm meeting, the first Privy Council this year, the King held his traditional face-to-face audience with PM Sunak at 5.45pm.
Both events took place at Buckingham Palace.
The King told the Prime Minister today he has had “so many wonderful messages and cards” that has “reduced him to tears.”
Lt Commander Will Thornton introduced the PM saying: “The Prime Minister, Your Majesty”.
Sunak walked across the room and shook the King’s hand firmly in first private audience since December.
And said: “Good evening Your Majesty, very nice to see you.
Charles said: “Bit of a gap”
Sunak replied: “A bit but wonderful to see you looking so well.”
The King replied: “Well, it’s all done by mirrors.”
They both laughed and Rishi said: “Well, we are all behind you, the country is behind you.”
Charles replied: “I’ve had so many wonderful messages and cards. Reduced me to tears most of the time.”
The pair then sat down for their private audience.
The King was last seen walking to church in Sandringham where he had been resting.
He has been this week in London and Windsor Castle.
But is expected to continue his recuperation from cancer treatment at Windsor and Highgrove, in coming weeks.
The King’s plan, drawn up after his operation for an enlarged prostate, was to return to work from today.
He is set to be out of action for several more weeks or even months while he is an out-patient at a London hospital where he is having treatment for cancer.
Princess Anne and Prince of Wales have both stood in at investitures for the King in recent weeks, according to the Court Circular official list royal engagements.
His last public engagement was a trip to the Royal Courts of Justice on December 14th.
The evening before, on December 13, he held his most recent Privy Council and audience with Prime Minister Rishi Sunak.
Charles spoke to the PM on the phone on Wednesday February 7 in a “goodwill” conversation rather than their weekly audience.
Prince William, 41, this morning handed out gongs at an investiture held at Windsor Castle.