I was reading some dreck about Prince William and Kate. It called them the Duke and Duchess of Cambridge. Later it referred to them as the Cambridges.
That can’t be correct, can it? Their last name, if one were to use it, is Windsor, isn’t it?
What is the correct address for them?
Prince William doesn’t have a last name. Not everyone does, some people even in America have a single name as their legal name.
He’s like Cher.
What’s on all their army ID in place of a last name?
When Louis XVI was overthrown, he wasn’t called Louis Bourbon, but, going back to the royal house’s founder, Louis Capet. Then they de-capetated him.
Royal people don’t generally use surnames in the sense that we’re used to. Will has a bunch of given names (William Arthur Philip Louis) and some titles, but that’s all.
Where a surname is needed, the place associated with a title is sometimes used. (So Cambridge in Will’s case.) His father Prince Charles (Prince of Wales) sometimes uses Wales as a surname, as did the late Princess Diana.
Windsor is the name of the royal house, but that’s not really a personal name. It’s just a label for the current dynasty.
Were they not Prince and Princess, but only Duke and Duchess, they would be Mountebatten-Windsors.
(emphasis mine)
Some military uniforms require a name badge/tag. It could be plastic, metal or cloth. I believe both William and Harry wear one that says “Wales” when required. That being said, in 1960, Queen Elizabeth had declared that her offsprings’ last names would be “Montbatten-Windsor” in situations where they needed a surname.
It sort of depends on how they’re addressed too. If their honorific is used, no last name is used. Example: His Royal Highness, William, Duke of Cambridge.
Missed the edit window.
The Duke of Cambridge’s full title is His Royal Highness The Duke of Cambridge KG KT.
In his military life, The Duke is known as Flight Lieutenant William Wales.
Both William and Harry use Wales as a surname when they need one. William was enrolled in college as William Wales, and was William Wales in the Royal Air Force (where his nickname was “Billy the Fish”). Prince Harry is known as Captain Harry Wales in the military.
Thread title edited for clarity.
Apparently on formal signatures, the Queen’s surname is “R”. Although it’s possible that this document was signed on Pirate Day. 
Privateer Day.
“R” isn’t really her surname. It’s more like signing it as “Elizabeth the Queen”.
Elizabeth R = Elizabeth Regina (i.e., Queen Elizabeth).
For male monarchs, R stands for Rex (king).
The Prince of Wales usually signs as Charles P (Charles Princeps = Prince Charles).
Victoria signed as Victoria RI (Victoria Regina Imperatrix = Queen-Empress).
“The Cambridges” is just journalistic shorthand for people who don’t have a true surname. “The Windsors” would be both incorrect and indeterminate, as lots of people in the royal family could be the intended subject.
You mean she uses “R” even when it’s not Talk-Like-a-Pirate Day? 
It’s actually more like signing it as a short form of Elizabeth II, Dei Gratia Magnae Britanniae, Hiberniae et terrarum transmarinarum quae in ditione sunt Britannica Regina, Fidei Defensor.
He specifically chose to retain “Wales” as his placeholder surname instead of switching to “Cambridge” after he got married (& was made a duke). His uncle, Prince Andrew, on the other hand went from being Lt. Windsor to Lt. York on his marriage (& being made Duke of York).
Right, remember the War of the Waleses? The same shorthand can be used to describe any peerage couple not just royals.
I think if it was Talk-Like-a-Pirate Day she’d sign “Elizabeth O.R.”, yeah?
But yes, the GQ answer (this is still in GQ, right?) is that it’s a short form for all you mention above.
There’s a lot of people who could be referred to as the “Waleses”, “Windsors”, and/or “Montbatten-Windsors”. But if you say the “Cambridges”, it’s pretty clear you’re referring to only 3 people.
Oh, does Queen Elizabeth and/or King Charles or William (presuming they goes with those names) have the power to to put Camilla in the tower of London or some other secure place?
See how much good that did for Anne Boleyn.
