The King’s meeting with Ursula von der Leyen following a post-Brexit deal over Northern Ireland was asked for by the EU Commission president, it is reported.
An agreement between Rishi Sunak and Von der Leyen was hailed as a “new chapter” in the fractious relationship between the UK and the EU.
But a meeting between Ms Von der Leyen and King Charles at Windsor Castle after the deal was sealed has led to controversy with Brexit supporters and the DUP accusing the government of dragging the monarch into a political row.
Buckingham Palace said that the meeting, where the King and the EU Commission president had tea together, took place on government advice.
And now a No10 insider has said that the meeting was called for by Ms Von der Leyen, reported The Sun.
It is claimed that Downing Street was more than happy to oblige with the EU chief wanting to see the monarch and she was photographed with Charles.
Meanwhile Mr Sunak’s spokesman Max Blain, said the government "would never" embroil the king in politics.
"His Majesty has met with a number of foreign leaders recently," he said, including Polish President Andrzej Duda and Ukraine's Volodymyr Zelensky. This is no different."
Earlier the agreement over Northern Ireland was called “historic” by Ms Von der Leyen and the prime minister called it a “decisive breakthrough”.
The new deal, dubbed the Windsor Framework, removes barriers on trade across the Irish Sea and hands a "veto" to politicians in Stormont on EU law - a set of concessions from Brussels that went further than some expected.
But it still includes a role for the European Court of Justice, with the Democratic Unionist Party and Tory backbenchers now set to study closely the details of the complex set of arrangements in the coming days.
Mr Sunak is expected to travel to Northern Ireland later and also talk to backbench MPs on Tuesday as he seeks to see off any rebellion from his own ranks.
But the reception so far has been warm, with DUP leader Sir Jeffrey Donaldson welcoming "significant progress" even as he warned that "there remain key issues of concern" regarding the deal. The view of the party will be crucial, if the deal is to help restore powersharing at Stormont.
MPs are expected to get a vote on the deal, but Downing Street has not so far said when or how such a vote might take place.
A key part of the deal is an emergency "Stormont brake" on changes to EU goods rules that can be pulled by the Northern Ireland Assembly, with No 10 hopeful that it will ensure concerns over a "democratic deficit" are addressed. The prime minister called it a "very powerful mechanism" for Stormont to use when it has concerns over EU law, as he heralded the overall deal as a "decisive breakthrough".
"Together we have changed the original protocol and are today announcing the new Windsor Framework," he said. "Today's agreement delivers smooth-flowing trade within the whole United Kingdom, protects Northern Ireland's place in our union and safeguards sovereignty for the people of Northern Ireland."
Leaders in the EU and beyond hailed the progress too, with Ms von der Leyen praising the "new chapter in our partnership" while French President Emmanuel Macron spoke of the "important decision".
US President Joe Biden said it was an "essential step" in protecting the Good Friday Agreement, while in Dublin Taoiseach Leo Varadkar said that the EU had moved "a lot" to facilitate a deal.
