The King has welcomed EU chief Ursula von der Leyen to Windsor Castle after she agreed to a historic post-Brexit deal for Northern Ireland.
Charles was pictured warmly shaking hands with the president of the European Commission at the royal residence on Monday afternoon before they were served tea.
Topics covered included climate change and the Russian invasion of Ukraine, but it is not known if Northern Ireland was on the agenda.
Ms Von der Leyen met Charles after holding a joint press conference with Rishi Sunak to unveil the deal, which the prime minister called a “decisive breakthrough”.
Some politicians earlier raised concerns that the monarch, who constitutionally is not supposed to be involved in political matters, was being pulled into the Brexit debate by the government, which could be creating an impression he was endorsing the deal.
Leading Conservative Brexiteer Jacob Rees-Mogg said it was wrong to involve Charles in the “immediate political controversy” on the day the deal was signed.
Baroness Arlene Foster, the former Democratic Unionist Party (DUP) leader and first minister of Northern Ireland, said the meeting in Windsor Castle was “crass”.
Buckingham Palace said Charles was acting on “the government’s advice”, but Downing Street said it was “fundamentally” a decision for the King.
There had been reports suggesting the meeting was arranged following a direct approach by the EU chief to Buckingham Palace, but this would be highly unusual as the normal channels of communication would go through the UK government.
A Buckingham Palace spokesman said: “The King is pleased to meet any world leader if they are visiting Britain and it is the government’s advice that he should do so.”
Downing Street defended the move to advise the King to meet Ms von der Leyen, saying Mr Sunak “fundamentally” believed the final decision was for Charles. “He firmly believes it’s for the King to make those decisions,” the prime minister’s official spokesman said.
He compared the Von der Leyen meeting to Charles talking to Poland’s Andrzej Duda or Ukraine’s president Volodymyr Zelensky.
Asked why the final protocol talks were taking place in Windsor, he said: “There are a number of occasions when these sorts of talks have been held in significant locations, this is no different.”
Mr Rees-Mogg, a former Cabinet minister, said earlier on Monday: “It is surprising that the King will meet Ursula Von der Leyen today as it antagonises the people the prime minister needs to conciliate. It is also constitutionally unwise to involve the King in a matter of immediate political controversy.”
Baroness Foster added: “I cannot quite believe that No 10 would ask HM the King to become involved in the finalising of a deal as controversial as this one. It’s crass and will go down very badly in NI. We must remember this is not the King’s decision but the government who it appears are tone deaf.”
Unveiling the new Northern Ireland trade deal on Monday, Mr Sunak said his “decisive breakthrough” will remove trade barriers and give the UK a “veto” on EU law.
The prime minister hailed the controversially named “Windsor Framework” as marking a “new chapter” on relations with Brussels that he hopes will restore powersharing in Stormont.
But European Commission president Ursula von der Leyen said the replacement to the Northern Ireland Protocol still includes a role for the European Court of Justice – a key issue for the Democratic Unionist Party (DUP).
The pair finalised the long-awaited deal to improve the agreement signed by Boris Johnson more than three years ago after a meeting in Windsor lasting under two hours.
