Let's keep it simple.
The Duchess of Cambridge is a princess by marriage. She is Princess William. She describes herself as a princess on two legal documents: the birth certificates of her children. Her husband is Prince William, Duke of Cambridge.
The Duchess of Cornwall is the Princess of Wales, a title she chooses not to use. Similarly she is Princess of Scotland, as she is husband of the Prince.
Only people who do not understand these things call them Princess Kate or Princess Camilla, and that includes a fair slice of the media. However, only people with issues go into denial about the fact they are princesses.
The word is courtesy, not curtsy.
The rule is that a woman takes on status, titles and styles of their husbands. Both Catherine and Camilla ARE princesses through marriage, but the stylings of royal duchesses are higher in rank than that of being princesses alone. The media should choose the higher-ranked styling, but the media is ignorant of etiquette protocols and just likes to use the title of princess....they find it "romantic" perhaps. And clueless people follow the media's example.
William is HRH Duke of Cambridge, Earl of Stratheran, Baron Carrickfergus, Prince William of Wales. Following etiquette protocols, Catherine is HRH, Duchess of Cambridge, Countess of Strathearn, Baroness Carrickfergus, Princess William of Wales. Catherine assumes her status through marriage and it is only a female born or bestowed a princess in her own right that uses the title with her own given name. People in the media do not come from the world knowledgeable about names, titles, styles etiquette.
Charles is Prince of Wales, Duke of Cornwall, Duke of Rothesay, Earl of Carrick, Earl of Chester, Baron Renfrew,Lord of the Isles and Prince and Great Steward of Scotland. Through marriage Camilla assumes all of these titles. She has chosen to honor the late Diana, Princess of Wales by being known as the Duchess of Cornwall instead, but ,Camilla IS Princess of Wales, Duchess or Cornwall, Duchess of Rothesay, Countess of Carrick, Countess of Chester, Baroness Renfrew, Princess and Great Steward of Scotland, Lady of the Isles the Princess CHARLES.
Most people are totally clueless about basic etiquette, much less more complex etiquette protocols. The media, unfortunately, is comprised of such people.
Daniel W comment "William has not been Prince William of Wales since his marriage.Royals sons of<father terriotoral designation>Sons lose it when they are given their own title and daughters on upon a marriage.William lost it in on the morning before his marriage.When he was created Duke of Cambridge..P.s to Bilbo...Zara and Peter were once called Prince/Princess ,when they were children.George /Charolette are of a curtsy rank and not a legitimacy rank like" Princess of Wales or Duchess of York"..."OF Cambridge "is nonroyal......
Catherine is not now, and never will be a "Princess". Only a woman born a Princess can use the title before their own given names, no matter what the media likes to call them.
On the occasion of his marriage, The Queen conferred a Dukedom on Prince William of Wales. The Duke received the titles of Duke of Cambridge, Earl of Strathearn and Baron Carrickfergus.
As a result, upon her marriage, Miss Catherine Middleton became Her Royal Highness, Princess William, Duchess of Cambridge, Countess of Strathearn and Lady Carrickfergus. In other words, she is a princess by marriage, and the "Princess William" title reflects that.
