With so many (like so many) rules that the Royal Family has to follow, it can be hard to keep track of them all. But, one rule that pretty much everyone knows is that the royals – and the public, for that matter – have to curtsy or bow to the monarchs.

As such, many royal fans were shocked when Kate Middleton didn’t curtsy to King Charles III at yesterday’s Commonwealth Day service, and they took to social media to question it. So, what’s the deal?

According to the royal rule book, female members of The Firm must curtsy to the most senior members of the monarchy – currently King Charles and Queen Consort Camilla – whilst their male counterparts must bow their heads. However, the gesture only needs to be carried out the first time that the royal sees the King or Queen that day.

As such, it seems that the Princess of Wales must have seen her in-laws ahead of the Commonwealth Day service and therefore didn’t need to curtsy when meeting them the second time around.

Karwai Tang – Getty Images

Previously speaking about the centuries-old tradition, Kate’s sister-in-law, Meghan Markle, admitted that she was surprised to find out that the family does it even behind closed doors. “I remember Harry and I were in the car and he says, ‘OK, well my grandmother’s going to be there so you’re going to meet her,” the Duchess of Sussex recalled during her history-making interview with Oprah Winfrey. “He goes, ‘Right, do you know how to curtsy?'”

That’s when Meghan admitted that she didn’t realise the Royal Family curtsied to each other when they weren’t in the public eye. “I thought genuinely that’s what happens outside, that was part of the fanfare, I didn’t think that’s what happens inside,” she added.