The King and Queen are about to embark on the most delicate royal visit to an ally in almost 70 years. When it was originally planned, few could have predicted that the United States would be at war, or that Britain would have refused permission for the US Air Force to use its British bases in its initial attack.

Certainly, no one could have foreseen that US War Secretary Pete Hegseth would have publicly sneered at the Royal Navy, or that President Trump would have claimed that the British Army had not seen front-line fighting in Iraq and Afghanistan (which he subsequently retracted.)

It will take all of King Charles's skill at diplomacy to ignore the regularly vicious language used by the President to describe Keir Starmer, as when he said that he was 'no Churchill'. A perfectly accurate statement, of course, but few prime ministers are, and Trump is no President Roosevelt.

With the US House Committee on Oversight and Government Reform demanding that Andrew Mountbatten-Windsor appear before it over the Epstein scandal, and serious issues still swirling regarding Peter Mandelson as the last ambassador to Washington, this is potentially one of the riskiest royal visits of modern times in political terms. 

Even at home there is uncertainty – with a poll by The Mail on Sunday suggesting that more than four in ten Britons believe the King and Queen should not undertake the four-day tour. One in four are undecided about it.

Fortunately, the King is this nation's greatest diplomatic asset. Although sometimes – and unfairly – maligned as weak or vacillating, the truth is we can rely upon Charles to be humorous, sure-footed and tenacious in dealing with the President. He is what you might call our Trump card.

The King, moreover, has a close historical precedent for what he is about to undertake on our behalf: that of his mother's visit to the United States shortly after the Suez Crisis of 1956.

There, too, a profound disagreement over the future of a key Middle Eastern strategic waterway had led to a rupture in the Special Relationship, with one ally denouncing the military operations embarked upon by the other.

On that occasion, the crisis led to the early retirement of the British Prime Minister, Sir Anthony Eden, in January 1957. His successor, Harold Macmillan, turned to Queen Elizabeth II, who had been on the throne for only five years, to restore good relations between the two countries. 

During only 15 hours in New York that October, the late Queen addressed the United Nations, attended a mayoral lunch of 1,500 people, then an English-Speaking Union dinner of 4,500 and a Commonwealth Ball of 4,500. 

One million people turned out to greet her in Washington and she had a chance to speak to President Eisenhower, and was both flattered and slightly shocked by the eagerness of the President to unburden himself to her about politics. By the end of the visit,

Macmillan was able to write that she had 'buried George III for good and all'. She had also buried the Suez Crisis in the minds of many Americans.

The fact that our monarchs are heads of state but also above politics give them a unique opportunity to interact with foreign politicians in a way that no one else can, and can prove invaluable at just such tricky diplomatic situations as in 1957, and today.

For all that he is intensely unpopular in Britain, President Trump revered the late Queen, respects the King, admires the monarchy, and had a British mother.

'He's fantastic and he has fought very hard,' Trump gushed about King Charles to Robert Hardman, author of Elizabeth II: In Private. In Public. The Inside Story. 'He's a fighter. We're close. I have a really good relationship with him.'

Trump's admiration for the King's fight against cancer is one of the reasons why this visit is likely to be a great success. He has already posted on Truth Social, that he is 'look[ing] forward to spending time with the King, whom I greatly respect. It will be TERRIFIC!'

The President might be willing to pick a fight with the Pope, but it is very unlikely that he would want to wreck the first royal state visit since May 2007 by repeating his threat to annex Canada, for example. When Trump did make those remarks in March 2025, the King was constitutionally unable to say anything publicly, but sent out subtle messages to anyone able to spot them, such as inviting Justin Trudeau to Sandringham, planting a maple tree in the garden of Buckingham Palace, and wearing Canadian orders and decorations on a visit to an aircraft carrier.

The King and Queen's schedule is slightly less hectic than Elizabeth II's was in 1957, reflecting the fact that he is 77 and she was only 31. They will be visiting Washington, New York and Virginia, attending a garden party, tea party and military review, before the King and Trump meet in private.

That is where our soft power will be subtly exerted in a way that would never work if we had an elected politician as president instead of an anointed monarch as king. Trump's rudeness in the Oval Office towards President Zelensky, Sanae Takaichi the Japanese premier, President Cyril Ramaphosa and others, will not be repeated to King Charles.

Meanwhile, Queen Camilla's meeting with representatives from campaign groups against domestic abuse and violence against women is a statement about what the couple really think of Andrew Mountbatten-Windsor.

It would be completely inappropriate for them to meet Epstein's victims, as the crimes had nothing whatever to do with them, and anyway there is a criminal investigation underway. There will be a state banquet at the White House and the King will address a joint meeting of the US Congress, the first British monarch to do so since his mother 35 years ago.

On each of these occasions, and their visit to the September 11 Memorial in New York, we can be certain that the royal couple will carry themselves with that innate sense of decorum and dignity that makes their country proud of them, and is in such stark contrast to the volatility and oafishness that their host occasionally displays.

The result of this visit will be a much strengthened Special Relationship, which is still so vital to Britain in terms of intelligence gathering, nuclear cooperation, trade and commerce, military hardware purchases, and so on.

Trump's uncoupling from Nato means that we must look to new strategic links, but we cannot immediately turn our back on an ally that still has 85,000 troops in Europe, however narcissistic and transactional its president.

King Charles has been underestimated throughout his life, but there is a tough core to him that will pull off this most diplomatically difficult of royal visits.

He and the Queen will triumph in America, and remind those Americans who have written us off as a country since Starmer became prime minister that we still have much to offer.

It will also remind us why we are so fortunate to have a monarchy, with King Charles and Queen Camilla at the head of it.

Lord Roberts of Belgravia's new book, Napoleon And His Marshals, is published in October.