When meeting a member of the British royal family, there are no obligatory rules for you to follow as a commoner (although, this is probably what you should do if you meet a royal!). Officially speaking, it’s simply a matter of respect and tradition. However, this does not hold true when it comes to interactions with the House of Windsor.
There are specific hierarchical rules laid out for the royal family that periodically change based on the situation. Meghan Markle’s case will be the same as Kate Middleton’s in some ways and different in others. For the sake of the rule exercise, we’ll fast forward to May 20, 2018, the day after Meghan Markle and Prince Harry’s wedding.
It all comes down to the Order of Precedence, the hierarchy of the royal family in terms of prominence. Meghan Markle, once she marries into the royal family, will be obliged to curtsy to royal family members above her in the Order, including the Queen, Prince Charles, Duchess Camilla, Prince William, any of the “blood princesses” (Anne, Alexandra, Beatrice, and Eugenie), and Kate Middleton.
Markle and Middleton entered the royal family in the same way, but Middleton has the slight edge because she married the future king. However, there is one exception for both Markle and Middleton that shakes up the Order. For both Middleton and Markle, when they are with their respective husbands, blood princesses Beatrice and Eugenie must curtsy to them.
Confused about who is who in the royal family? Take a look at this royal family tree to get up to speed.