It’s time to settle this, once and for all!

By Michelle Tauber and Simon Perry
Updated September 07, 2017
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kate middleton duchess of cambridge
You may recognize the ring on Kate Middleton’s finger as the same one Prince William’s mother Diana was given by his father, Prince Charles. After proposing in 2010, William said part of the reason he used his mother's ring is because he didn’t want her to “miss out on” the day.
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This content originally appeared on People.

More than six years after Kate Middleton married Prince William, the debate rages on: Is she now Princess Kate or Duchess Catherine?

Our sister site (and royals' experts), PEOPLE.com chooses to refer to her as Princess Kate. But in recent stories about Kate/Catherine/George and Charlotte’s mom, some readers have lit up the comments section in regard to the choice of moniker.

While both duchess and princess are both acceptable for conversation and the written word, we wanted to delve deeper into the princess vs. duchess debate.

Strictly speaking, she is neither a princess nor a Kate. Growing up in the English village of Bucklebury, she was known as Catherine among her friends and family. But by the time she went to St. Andrews University, where she met William, she was widely known as “Kate.”

Now, she is officially Catherine—“Catherine and I,” William regularly says in speeches—and the palace calls her Catherine as well.

As for the second part, her proper title along with William is TRH Duke and Duchess of Cambridge. (“TRH” stands for “Their Royal Highnesses.”) It was given to William on their wedding day, and by definition, as soon as Kate said “I do,” she became the duchess.

To complicate matters, the young royals are known as something different in Scotland: the Earl and Countess of Strathearn, titles they were awarded by Her Majesty Queen Elizabeth. William also has an Irish title, Baron Carrickfergus. (Say that three times fast.) And here’s where things get really sticky: If Kate hadn’t been given the Cambridge title, she would be Princess William of Wales.

“Yes, she is a princess,” says Majesty managing editor Joe Little. “I would say that if you marry a prince, you are a princess.” It would seem that William agrees: On the register of Prince George’s birth, Catherine has the fairy tale-sounding title, “Princess of the United Kingdom.”

Historically, there has been so much title confusion that some misusage simply drifts into the mainstream: William’s mother, Diana, was officially the Princess of Wales “but everywhere, you have Princess Diana,” says Little. “I have even seen that used at Kensington Palace.”

And what about last names, you say? A palace source says that for the most part, members of the royal family who are entitled to “the style and dignity of HRH Prince or Princess do not need a surname, but if at any time any of them do need a surname (such as upon marriage), that surname is Mountbatten-Windsor.”

But this is a family where names are in what Little calls a “permanent state of flux.” Whereas most blue-blood clans would carry the Mountbatten-Windsor name throughout their line, William’s father, Prince Charles, is known as Wales, Princesses Beatrice and Eugenie are surnamed York after their parents, the Duke and Duchess of York and the Wessex children are known as Wessex and so on.

So, William was known as William Wales during his school years at Eton and St. Andrews, and as Captain Wales in the army. (Although his rank in the Royal Air Force was the equivalent of captain, he was known as Flight Lieutenant Wales.)

Of course, we have a feeling we know which title Kate herself prefers: Mummy.