At last, in our bewildering world, there is reassuring news. A sinister buffoon may be about to become the most powerful man in the free world, our country may be staggering cluelessly into an uncertain future, Ed Balls may have become a cosy national treasure, but, in one area at least, the old standards are being maintained. Members of the royal family are still behaving like twits. Until this past weekend, some of us may not have known or cared about Princess Beatrice. Is she the one who looms up at Royal Ascot in a silly hat? Or was she filmed doing something dodgy with the “Fake Sheikh”?

Now we know. Princess Beatrice is the daughter of Sarah Ferguson, Duchess of York. She has just carved her name in the history books by stabbing the singer Ed Sheeran in the cheek. At a party at the Royal Lodge in Windsor, another pop star James Blunt joked that he would like to be knighted. Mock knightings turn out to be quite the thing at royal parties, apparently – it was one of Fergie’s favourite japes – and so Princess Beatrice reached for a ceremonial sword, raised it high over her head, and slashed pop’s ginger man in the face.

At a time when there has been a dearth of royal madcap stories – Prince William and the Duchess of Cambridge are decorative but dull, Prince Harry is behaving himself, Prince Charles is mellowing – the “princess stabs pop star” story represents something of a return to form. The British public expect at least some of the royal family to make fools of themselves. It is largely what they are there for. They are court jesters to the nation.

Beatrice is following a family tradition – her great-aunt Margaret enjoyed the company of a professional criminal

Indeed, Princess Beatrice is following something of a family tradition. One of Prince Andrew’s female guests at his country house has revealed that she was awoken one morning by the prince bursting into her room, pointing a fire extinguisher at her and roaring with laughter. He never tired of playing the trick on female guests, she was later told. Beatrice’s great-aunt Margaret famously enjoyed the company of the professional criminal John Bindon. At a party – attended by Her Royal Highness – on the West Indian island of Mustique, “Big John” amused her by hanging five half-pint beer mugs on the appendage that gave him his nickname.

A nation slightly less brainwashed about royalty might have occasionally questioned whether the antics of these people were worthy of public attention – and money – but, as the career of Fergie has shown, you can get away with pretty much anything if you are connected to the royal family. From toe-sucking to acting as ambassador for Weightwatchers, from starring in a reality show set on a housing estate to asking a News of the World man for £500,000 for access to Prince Andrew, she has been a gift to the press and to authors.

In the mid-1980s, I wrote a book with Willie Donaldson to mark the marriage of Prince Andrew and Fergie. Called 101 Things You Didn’t Know About the Royal Lovebirds, it was written under the name of Talbot Church, a court correspondent who called himself “the man the royals trust”. It was meant to be a parody of tabloid journalism – prurient, snobbish, ill-informed and, above all, absurd.

The problem, we quickly discovered, was that people, and indeed much of the press, will believe anything about the royals. Among the 101 things revealed was a story that Fergie had once been arrested in a New Orleans brothel, having mistaken it for a hotel. Her Romeo prince was so impervious to pain that on one occasion, during Prince Charles’s mystical phase, he startled his brother by levitating over a lighted gas ring.

The stories were run by the Sun as fact. One anecdote found its way into Kitty Kelley’s biography of Prince Philip. When, years later, Talbot returned to cover the wedding of Prince William and Kate Middleton, the same thing happened. I wrote that the Duke of Edinburgh suffered from a rare condition called “royal Tourette syndrome”, and that three equerries had been given the responsibility of keeping him away from President Obama. The next day, Paul Dacre, editor of the Daily Mail, furiously asked his journalists how they had missed the story.

Fiction blurs effortlessly into fact when it comes to the royal family. They were post-truth long before it became fashionable.