Royal Protocol states that members of the royal family are expected to always curtsy when greeting Queen Elizabeth, but some royal fans were shocked when Kate Middleton and Camilla Parker Bowles appeared not to do so during the annual Trooping the Color event.

According to Express UK, as the Duchesses of Cambridge and Cornwall arrived on the balcony of Buckingham Palace for the event and awaited the Queen’s arrival, they notably did not curtsy as her carriage pulled in past the gates—even as Sophie, Countess of Wessex and her daughter, Lady Louise Windsor, did.

Though both Middleton and Parker Bowles are married to the next two future Kings of England, they are still expected to curtsy to the Queen during formal engagements, which was why their decision not to curtsy to the Queen at this particular event seemed like a surprise. However, it is worth noting that there are not always specific rules in place, and if they had previously curtsied to Her Majesty at their first meeting, they may not have been required to do so a second time.

The rule of royal curtsy etiquette is considered to be a little complicated beyond everyone making sure that they show respect to the Queen, as it was changed twice in recent years. After Prince Charles married Parker-Bowles in 2005, and again after Prince William married Middleton in 2011, the Queen had the protocols changed.

In the new set of rules, whenever the Duchess of Cornwall or Duchess of Cambridge attend events without their husbands, they are expected to still curtsy to “Blood princesses” who are further down the line of hierarchy. These include Anne, Princess Royal, Princess Alexandra, Princess Eugenie and Princess Beatrice.

However, when Middleton attends an event with her husband, the royal cousins then have to bend the knee to her because she assumes her husband’s rank. Regardless of whether her husband is at an event or not, Middleton must curtsy to the Queen and Prince Philip, as well as Charles and Camilla.

Markle, who is technically a junior royal, is expected to always curtsy to her sister-in-law.

Queen Elizabeth II, Prince Charles, Prince William, Prince Harry, Kate Middleton, Camilla Parker Bowles Meghan Markle
Prince Charles, Prince Andrew, Camilla Parker Bowles, Queen Elizabeth II, Meghan Markle, Prince Harry, Prince William and Kate Middleton watch the RAF flypast on the balcony of Buckingham Palace on July 10, 2018 in London. Getty Images/Chris Jackson