Duke and Duchess of Cambridge?

[Paul Henry]

Whilst it's not technically correct to say Princess Kate, it's what I'm sure most people will call her, including yours truly. You can't be sent to the tower or beheaded for saying it, so what's the problem?

If she had married a Mr. William Wales, which in a sense she did, as that is the surname that Prince William actually uses as a member of the armed forces, she would not now be called Mrs. William Wales but Mrs. Catherine Wales, because the style of the wife using the husband's first name is entirely obsolete in England today, and has been for many, many years*, regardless of whatever anyone might say to the contrary. Anyone using that form of address would be laughed at. For this precise reason I would rather die than refer to her as Princess William, as to do so would be 'social death', whatever even the Palace may pronounce on the subject.

So, it is just as well she also has another title, as in the unlikely event that it was necessary to refer to HRH Kate (LOL!) in the presence of the Queen, for example, the only acceptable way out of the conundrum would be to refer to her as the Duchess of Cambridge. I have met Prince Phillip, Duke of Edinburgh, BTW, although never the Queen herself or any other member of the royal family, so the unlikely is not necessarily the impossible.

*ETA: Many, many years in this case meaning within my lifetime, and probably at least those of my parents, who are in their eighties.

My emboldening
It's not entirely obsolete, it's unusual perahps but I still know of many wives who are known as Mrs - husbands name,My mother generally prefers to be known in that fashion, although she is in her late seventies.
No one laughs at that form of address, and hardly social death either