Before he came to the throne, the then Prince Charles had been challenged over whether he could avoid meddling and stay out of politics when he became King.

Now King Charles seems to be in demand as never before to help out the politicians and to get involved, playing an unexpectedly pivotal role in dramatic times for international diplomacy.

Last week an invitation from the King for a second state visit was offered to President Trump, with UK Prime Minister Sir Keir Starmer presenting it, with no shortage of flattery, as an “unprecedented” sign of friendship and respect.

Then in the fallout of the disastrous Trump meeting with President Zelensky in the White House, it was the King, as well as Sir Keir, who embraced the Ukrainian leader and offered a visible image of support for his embattled country.

It was a vital element in the diplomatic balancing act taking place, as the UK government tries to shore up Western support for Ukraine, without alienating and aggravating the Trump administration in the US.

It’s placed the double act of King Charles and Sir Keir Starmer at the centre of some huge shifts in international relations.

The King greeting President Zelensky so warmly and publicly, on a visit to Sandringham, was an important message of solidarity that he had not been abandoned and that there was still support for Ukraine, three years after it was invaded by Russia.

With Trump’s enthusiasm for the royals, and his evident keenness for a state visit, it provides a diplomatic bridge, with the King keeping open friendly channels with both Trump and Zelensky.

Trump described the King as a “beautiful man”, as he looked forward to the opulence of a state visit, with its carriage ride up the Mall and glittering banquet. Invitations for such visits are sent by the monarch, but the decisions on who gets invited are made in government.

The King has decades of experience of getting along with people from remarkably different backgrounds and viewpoints. He seems to enjoy chatting to people, asking them about themselves, while saying little about his own views. He’s also known generations of previous US leaders, all the way back to visiting Nixon in the White House and meeting Eisenhower at Balmoral.

For King Charles, there has also been a very personal sense of support for Ukraine, he’s been outspoken in a way that is unusual. He has attacked the “indescribable aggression” against Ukraine, in what he called an “unprovoked attack on their land”.

Soon after the invasion he went to see refugees arriving in Romania. On visits to France and Germany he singled out the importance of Western allies standing firm with Ukraine to protect democratic values.

He’s made repeated visits to meet the Ukrainian community in the UK and last month went to see a project providing medical assistance for injured Ukrainian military personnel.

But these are complicated times for the monarch, not least because as well as being the UK’s head of state, King Charles is also the head of state of Canada – and on Monday he faced a different set of agendas when he met Canada’s Prime Minister Justin Trudeau.

The words exchanged in those meetings are not revealed – but as well as discussing Ukraine, there would be no need to guess the other topic of conversation.

“Nothing seems more important to Canadians right now than standing up for our sovereignty and our independence as a nation,” said Trudeau ahead of the meeting.

Canada is facing President Trump’s calls for his northern neighbour, and longstanding Nato ally, to become the 51st state of the US. This unsurprisingly has deeply angered and offended many Canadians.

They might look to King Charles as their head of state, and head of the Commonwealth too, to strongly speak up for them and to rebuff such expansionist claims from the US president.

Except that from a UK perspective, the King is being deployed to keep President Trump on board and to keep alive the “special relationship” between the US and UK. So there will be no appetite for a royal denunciation over Canada.

The BBC’s Royalwatch newsletter has already had plenty of feedback from Canadians who are angry that the King has not spoken up for them against Trump.

“I am a 73-year-old proud Canadian and loyal royal supporter. Should the King choose a relationship with Trump over support of Canada, I will be changing my support to withdrawing from the Commonwealth,” emailed Peggy.

“I realise the Royal Family don’t usually get involved in politics, but this is different and at the moment many here are wondering why we have a King as head of state at all,” Ann said in an email to the newsletter.

‌It won’t be an easy balancing act, when so much of the King’s diplomacy has to be in symbols as much as words. He has to speak on the advice of ministers, in Canada and the UK.

It seems like a long time since one of the famous moments of unspoken royal commentary, when the late Queen Elizabeth II stood in front of a big bunch of flowers in the Ukrainian colours of blue and yellow, in the weeks after the Russian invasion.

And who was she meeting? A popular young Canadian prime minister called Justin Trudeau. It was seen as a sign of Western solidarity to support Ukraine.

Would anyone have believed three years later that he’d be seeking support against the United States?