It’s a tricky one. On the one hand, it’s perfectly routine for the head of state to meet a visiting foreign dignitary. When President Cyril Ramaphosa of South Africa popped over to London for the first state visit of the reign of King Charles III no one complained about the monarch being sullied with politics or being used for nefarious purposes. Ursula von der Leyen, President of the Commission of the European Union, paying a courtesy visit to see the king at Windsor Castle is a different matter, it seems. The problem is obvious. She’s coming over to settle the last major outstanding bit of Brexit business with the prime minister, and not everyone is happy about what’s being proposed (whether they’ve actually read the text yet or not).

The political talks just happen to be taking place at a hotel in Windsor, and so, given the proximity, it would seem rude for her not to come round for tea, and equally rude for his majesty not to invite the representative of Britain’s closest trading partner to have a little audience.

As it happens, the country, including most of its politicians, is so desperate to finally get Brexit done and never hear the word “protocol” again (outside the context of spy movies), that they’d be content to have his majesty take the knee and sing Beethoven’s Ode to Joy in the original German if it would mean the end of the matter.

Rishi Sunak, the king, von der Leyen and everyone else concerned are also fortunate that the deal, at least according to the carefully crafted spin, seems to be a genuine breakthrough. It has already won the backing of Labour; and, even more valuable than Charles’ imprimatur, Steve Baker, Northern Ireland Office minister and one-time leader of the hard-line Eurosceptic “Spartans”, has blessed it: “I can only say this, the prime minister is on the cusp of securing a really fantastic result for everyone involved.”

There are some who remain perturbed by the involvement of the king, such as former Northern Ireland DUP leader Arlene Foster and Nigel Farage, whose royalism only extends as far as own prejudices. But the Sunak deal is sufficiently cross-party and consensual that it shouldn’t tarnish the traditional royal neutrality in party political matters. It is mainstream.

Then again, what is mainstream one year can look very different if circumstances change. The only remotely comparable argument about the monarch getting tangled up in controversial diplomacy and thus politics was when King George VI and the Queen invited Neville Chamberlain and his wife to appear on the balcony of Buckingham Palace, in 1938. Chamberlain had just returned from meeting Adolf Hitler in Germany with the famous “piece of paper”, and a promise of “peace in our time”. A few days earlier it seemed war was inevitable, with all the horrors that entitled. Gas masks were being issued. The relief at the news of a peace agreement seized the nation, and the king and queen, and, presumably the 12-year old Princess Elizabeth, were no exceptions. Mothers felt that Chamberlain had saved the lives of their boys, and given them their sons back. The crowds that gathered in Downing Street and then the Mall in the evening were ecstatic, and understandably so. Winston Churchill was one of the few to warn of the abiding and growing danger presented by the dictators. Of course, we know what happened next. However, the prestige of the monarchy, then just recovering from the abdication crisis and departure of Edward VIII in 1936, survived this mistake. Perhaps the public concluded that the king and queen had merely fallen for the same vain hopes for peace as the rest of the country.

The parallels with today are superficially attractive, but the Northern Ireland Protocol is not the Munich Agreement to dismember Czechoslovakia, and Ursula von der Leyen isn’t Hitler. Even if the Sunak deal goes horribly wrong, it’s not going to change anyone’s mind about the monarchy.