The King and President Joe Biden were all smiles and warm handshakes as the UK-US special relationship looked to be on a firm footing.
Charles hosted President Biden for tea and talks, in his private Windsor Castle sitting room, which lasted about 20 minutes – and they also viewed US-related items from the Royal Collection.
Ahead of the meeting, it was reported climate change was due to be discussed, and at the conclusion of their talks the King and the president joined delegates from the Climate Finance Mobilisation Forum who met at the castle.
Mr Biden’s whirlwind visit to the UK had begun with a meeting with Prime Minister Rishi Sunak in Downing Street – with the American leader hailing the “rock-solid” relationship between the US and the UK.
A fleet of helicopters carrying the president – whose aircraft has the call sign Marine One – his entourage, security and travelling White House press corps landed on Windsor Castle’s east terrace around 10 minutes before formalities began.
Charles stepped from a dais to meet the president as the door of a large chauffeur driven vehicle, which had swept onto the castle’s quadrangle, was opened.
The King warmly greeted the American leader, shaking hands with Mr Biden as a guard of honour stood nearby.
As the two men exchanged a few words while still shaking hands, Mr Biden touched the King’s right arm with his free hand and Charles returned the gesture.
The King and the president last met on the eve of the late Queen’s funeral last September, when a reception was held for dignitaries ahead of the national event.
The visit to Windsor was part of a busy day for the president, who is making a layover in London on the way to the Nato summit in Vilnius, Lithuania.
It had all the trappings of a more formal state visit, with a private exchange of gifts, alongside the tea and viewing of the mini-display of Royal Collection items.
A spokesperson for the King said about the Windsor Castle event: “An extremely cordial and successful meeting that touched on a wide variety of issues of mutual interest and concern.
“You will have seen for yourselves the personal warmth between His Majesty and the president.”
The pomp and pageantry saw the president, joined by the King, inspect a Guard of Honour formed of The Prince of Wales’s Company from the Welsh Guards.
The two heads of state then watched the Guardsmen and officers march off the quadrangle before they sat down to tea in the castle’s oak room.