Kat with a K

The Princess Problem, or Why She's a Princess but Not Princess Kate

It's true: The new Duchess of Cambridge is NOT Princess Catherine. But things are a bit more complex than Matt Yglesias's fun flowchart shows, and she IS a princess. The complicating factor is that Britain treats two types of princesses differently: there are princesses of the blood and princesses by marriage.

Princesses of the blood are a sovereign's legitimate daughters and male-line granddaughters; they are styled Her Royal Highness Princess [name], followed by any other titles. The current princesses of the blood are Princess Alexandra of Kent (the Queen's first cousin; a male-line granddaughter of George V), Princess Anne (the Queen's daughter), Princesses Beatrice and Eugenie of York (Prince Andrew's daughters), and Prince Edward's daughter Louise. To make things difficult, her parents have opted to style her as the daughter of an earl, so she goes by The Lady Louise Mountbatten-Windsor, but legally, she's still HRH Princess Louise of Wessex. (Princess Anne's daughter, because she's female-line, is still in line for the throne but has no title, so she's just Zara Phillips.)

Princesses by marriage, on the other hand, are princesses but are NOT called Princess [name]. They are the wives of a sovereign's sons and male-line grandsons. They are styled HRH Princess [husband's name]. Example: the wife of the Queen's cousin Prince Michael of Kent is named Princess Michael of Kent. If the husband has other titles as well, the female version of those titles comes after, and in these cases, they tend to go by the other title, but "princess" is still there, legally. So Prince Edward's wife is usually called HRH Sophie, Countess of Wessex, but legally, she's HRH Princess Edward Antony Richard Louis, Countess of Wessex, Viscountess Severn, etc. (Edward has lots of titles.)

An exception: The wife of the Prince of Wales gets Princess of Wales after her name as a secondary title, but she is still not Princess [name]. So Camilla is legally HRH Princess Charles Philip Arthur George, Princess of Wales, Duchess of Cornwall, etc., but she usually goes by HRH Camilla, Duchess of Cornwall, because people associate "Princess of Wales" so strongly with Diana. Diana herself was never actually "Princess Diana," even though everyone called her that. When she was married, she was HRH Princess Charles etc., as above. When Prince Charles (and Prince Andrew) divorced, the Queen made a law that princesses by marriage who divorced lost the HRH. That made Prince Andrew's ex-wife just Sarah, Duchess of York, but since Charles is Prince of Wales, Diana became Diana, Princess of Wales (without the HRH). I believe that made her the only non-royal British princess ever.

So, to sum up: today's bride will usually go by HRH Catherine, Duchess of Cambridge, but legally she is HRH Princess William Arthur Philip Louis, Duchess of Cambridge, Countess of Strathearn, Baroness Carrickfergus, MA. (And I try to remember to include the MA, since that one's all hers.)