To become a princess, you have to marry a prince. So why are we calling Kate Middleton and Meghan Markle Duchesses when they both married princes?
In addition to marrying a prince, another way to become a princess is if your father is a prince. That is why Prince William and Kate Middleton’s second child is Princess Charlotte.
When Kate Middleton married Prince William, she received titles the Duchess of Cambridge and Princess William of Wales. That makes her a princess, just like Meghan Markle, whose titles are Duchess of Sussex, Princess Harry of Wales.
Prince Andrew’s daughters also have title princess before their name – Princess Beatrice and Princess Eugenie. However, Zara Phillips, the daughter of Princess Anne doesn’t have the title princess, just like Louise Windsor, Prince Edward’s daughter, because Princess Anne and Prince Edward decided to go against bestowing their children with the title.
Lucy Hume, associate director of Debrett’s shared with Town and Country, “The monarch may offer to bestow a royal title upon his or her daughter’s children. For Peter and Zara Phillips, the Queen offered to give them a royal title when they were born, but Princess Anne and Captain Phillips opted to decline this offer.”
Source: rd.com