Kate Middleton, Meghan Markle
Catherine, The Duchess of Cambridge stands with Meghan, Duchess of Sussex at Westminster Abbey for a Commonwealth day service on March 11, 2019, in London, England. Getty Images/Richard Pohle

Duchesses Kate Middleton and Meghan Markle have to follow strict royal protocol and guidelines at all times when attending royal engagements, and they also need to watch their words.

However, a self-styled royal expert recently claimed that Markle and Middleton are given a list of taboo words that they can never say in public. Daniela Esler wrote in an opinion piece for News.com that members of the royal family are discouraged from asking for the "toilet" in public and saying "pardon."

“What you need to ask for is the loo, as toilet is not used by the royals as it is derived from a French word," Esler wrote. "Similarly, the Royal Family never has to utter mortgage, annual leave and bin night. Pardon is off limits. Reportedly, the Windsors and their ilk of landed aristocrats who value good tweed and a well-bred terrier use sorry, or sorry, what?"

The self-styled royal expert went on to say that when Markle will be setting up her and Prince Harry's living room in Frogmore Cottage, she may also need to watch out for certain forbidden words. Esler wrote that royal palaces only have "sofas" as the word couch is apparently a "wee bit common."

As for meals, Esler said that the Duchess of Cambridge and Duchess of Sussex would say "pudding" rather than the "decidedly declasse dessert.” It is also claimed that "scent" is preferred over "perfume," another French-derived word.

Meanwhile, Markle is often described as a royal rule-breaker due to reports claiming she broke royal tradition in multiple occasions. However, since there is no official rule book, the duchess has gotten away with challenging the way things have been done in the British royal family.

Back in December, the pregnant duchess reportedly broke tradition when she wore dark nail polish while presenting at The Fashion Awards. Members of the royal family apparently usually wear the lightest of pinks or neutrals, and Markle's bordeaux nail polish is not at all common, according to Glamour.

Markle also defied royal protocol when she took off her wedges at Bondi Beach during her and Prince Harry's royal tour of Australia, Fiji, Tonga and New Zealand. Royals are required to keep their shoes on at all times, especially when visiting other countries.

The former "Suits" star apparently also broke a rule when she joined Prince Harry at a charity performance of "Hamilton" back in August 2018. Markle showed off her bare legs in a black Judith & Charles tuxedo dress without wearing any stockings.