
On Wednesday, September 17, Donald and Melania Trump arrived at Windsor Castle by helicopter, where they were greeted by Princess Kate, Prince William, King Charles, and Queen Camilla. Royal fans were quick to notice that neither Kate nor Melania curtsied to King Charles, with some commenters suggesting the pair had broken royal protocol in the process.
The Princess of Wales usually curtsies to King Charles, but her decision to be more informal during the arrival of their U.S. visitors apparently doesn't break official protocol. Melania's decision to forego the formality of curtsying also isn't in opposition to any specific guidance, either.
As noted by the Royal Family's official website, "There are no obligatory codes of behavior when meeting The Queen or a member of the Royal Family, but many people wish to observe the traditional forms."

The Royal Family's website also details the traditional customs often carried out by people meeting The King and Queen. "For men this is a neck bow (from the head only) whilst women do a small curtsy," the guidelines noted. "Other people prefer simply to shake hands in the usual way."
Along with curtsying, there are numerous ways visitors are expected to behave while addressing the royals. "On presentation to The Queen, the correct formal address is 'Your Majesty' and subsequently 'Ma'am,' pronounced with a short 'a,' as in 'jam,'" the Royal Family's site explained. "For male members of the Royal Family the same rules apply, with the title used in the first instance being 'Your Royal Highness' and subsequently 'Sir.'"

Meanwhile, People suggested that Princess Kate "likely didn't curtsy publicly because she had already greeted King Charles and Queen Camilla" prior to the arrival of the Trumps. Whether or not this was the case, it seems as though a certain degree of informality is in place for the U.S. state visit.