Why Was Princess Diana Called Princess But Not Kate Middleton?

British royal titles can be a bit confusing, even for those who follow the family regularly. For example, Queen Elizabeth's husband was always called Prince Philip rather than king, as he was married to the queen but not the reigning monarch and never in line for the throne. In fact, he was called the Duke of Edinburgh before the queen bestowed the prince title on him in 1957, according to CBS News. He kept both titles until his death in 2021.

There is also much confusion as to why Diana Spencer was called Princess Diana after she married Prince Charles, but Kate Middleton — who married Charles' son, Prince William — is just known as Kate Middleton, or the Duchess of Cambridge. Queen Elizabeth gave her when she married William, who was given the title the Duke of Cambridge himself. So, why would one woman who married a British prince be called a princess but another is not?

Neither Diana or Kate were princesses at birth

It turns out that Princess Diana was called just that — Princess Diana — but technically, she was not a princess for some detailed reasons. True princesses are born to the royal family, which is why Prince William and Kate Middleton's daughter, Charlotte, is called Princess Charlotte. Diana married into the royal family, and did receive a title from Queen Elizabeth, but it wasn't Princess Diana. Instead, she was officially "Her Royal Highness, The Princess of Wales" or "Diana, Princess of Wales" (via Metro).

If the word "princess" officially came before her given name, then Diana would have been a real princess, but that also would have required her to have been born into the royal family. Instead, it was the public that bestowed the title "Princess Diana" upon her and it stuck. 

Even Kate's official royal name is not just the Duchess of Cambridge. If one wanted to call her by all of her titles, William's wife would technically be "Her Royal Highness The Duchess Of Cambridge, Countess Of Strathearn and Lady Carrickfergus." Now, that's a mouthful and likely why she is colloquially just known as "Kate."