Prince William's bizarre royal superstition prevents him from eating certain food

A specific form of food is reportedly banned from the Prince and Princess of Wales' royal residence, as part of a long-standing superstition.

As followers of the world's most famous family will likely already know by now, what members of the monarchy are served for their breakfast, lunch and dinner is a decision not taken lightly by palace chefs.

Tyla reported last year, these cooking connoisseurs have a strict list of ingredients they have to avoid when it comes to King Charles III specifically - including items that could trigger food poisoning, like shellfish.

"It is a very sensible move to abandon having seafood when out and about on public duties. We don't want a member of the Royal Family having a serious reaction to food poisoning. Especially if [they] are on an overseas tour," Grant Harrold, a former Royal butler, told the Express in June.

"Therefore, you will not normally find this on the royal menu."

Several food groups are reportedly banned (Max Mumby/Indigo/Getty Images)

It isn't just The King that palace chefs have to pay particular attention to during mealtimes, however, but his descendants, particularly Prince William, who is said to be a bit funny about one specific food.

Well, not the food itself, but the way it's presented - and according to former royal chef Graham Newbould, it has nothing to do with health risks.

Appearing previously on the TV documentary, Secrets of the Royal Kitchen, he explained: "The royals never have square sandwiches because tradition has it that anyone presenting them with pointed-edged food is trying to overthrow the throne of England."

Yep, that's right - apparently, despite being a father-of-three, William kicks up quite the fuss if he's served any sandwiches with 90-degree edges.

The superstition is also said to extend to his wife, Kate Middleton, who is said to have taken on her husband's peculiar fears.

Square sarnies are reportedly a no-go (Getty Stock Image)

Newbould spent two years working under The Queen and (then) Prince Charles at Buckingham Palace, before moving on to work with the Wales' at Kensington Palace for a further six.

Never once, he claims, did he whip up a square or rectangular sandwich, having been warned by his predecessor, as per The Express.

The Queen, the chef added specifically, was a fan of something known as a 'jam penny', a round sandwich filled with jam and cream, with the crusts having been removed to create the shape.

During his time under the royals, Newbould also learned that The late Queen's great-grandmother, Queen Victoria's husband Prince Albert was just as suspicious as William when it came to shapes.

Apparently, he'd avoid anything shaped like a coffin, so as not to bring on his own demise.

The more you know, eh?