Meghan Markle's Gorgeous Dior Dress Just Broke A Royal Fashion Rule

Maija Kappler
The Duke and Duchess of Cambridge arrive with the Duke and Duchess of Sussex to the RAF Centenary at Westminster Abbey, London.

You probably won't be surprised to learn that the two royal duchesses formerly known as Meghan Markle and Kate Middleton looked gorgeous at a royal event today.

But did you know the Duchess of Sussex's black Dior dress may have broken a Royal Family fashion rule?

On Tuesday, the day after Prince Louis' christening, Catherine, Duchess of Cambridge and Meghan, Duchess of Sussex joined their husbands, along with Queen Elizabeth, Prince Charles and Duchess Camilla, at the 100th celebration of the Royal Air Force.

Meghan wore what's quickly becoming her signature style: a simple, elegant boatneck dress. But by choosing to wear black, she was flouting a royal fashion rule: royals are not supposed to wear black to events unless they're in mourning.

Meghan, Duchess of Sussex during the RAF Centenary at Westminster Abbey, London.

But those rules might be loosening up a bit, a British etiquette expert told InStyle.

As a fashion icon, Princess Diana was considered an exception to the rule, Alexandra Messervy, founder of The English Manner, explained to the site. And Meghan has in fact worn black before, and hasn't faced a huge amount of outcry, except from the most staunch traditionalists.

(UPDATE: It's worth noting that some outlets are calling the colour of the dress "deep navy," although Harper's Bazaar and InStyle both called it black. Without an official statement from the palace or Dior, it remains a matter of debate, and, possibly, screen settings.)