Some sharp-eyed royal fans noticed that Princess Kate did not bow to King Charles at the Commonwealth Day ceremony in London on March 13.

But before you start fussing about what this means, this is simply a matter of protocol.

All members of the royal family are supposed to bow to the king and queen, but they bow only once a day, when they first meet the king and queen. [OK! says that Kate did not bow to her father-in-law, presumably because she had left with him earlier that day.

This trivia aside, Commonwealth Day is an official day designated to celebrate the Commonwealth and all its member states. It generally falls on the second Monday in March, and is celebrated at Westminster Abbey with a service attended by senior royals.

On this day, the Princess of Wales wore an elegant ensemble by Erdem, which, according to People, she paired with navy pointed pumps, an embellished navy hat, and a Prince of Wales feather brooch given to her by the King.