Yes, that's a bit of a trick question because, while he does have a surname he whips out on occasion (surely his schoolmasters and Royal Air Force commanders needed something to bark at him other than "Your Highness!"), he is predominantly known by his formal title.
And while we tend to familiarly call his wife by her maiden name, Kate Middleton, she is for all intents and purposes Catherine, Duchess of Cambridge. So what, exactly, is the littlest HRH's surname?
When utilizing a surname like ordinary folks, William and his brother, Prince Harry, (and now Prince George!) take a cue from father Charles, Prince of Wales' royal house and go by William Wales and Harry Wales.
Now, presumably, William and Kate's firstborn son (and the same goes for subsequent brothers and sisters) will one day find himself in a situation where the ole Prince So-and-So won't quite fit the circumstances. So, what will the the kid go by in order to seem more like an, er, ordinary person?
Well, it turns out that his or her surname is actually up to mum and dad—and they have three choices.
According to BBC News, the royal baby's last name could be Wales, like dad; Cambridge, like the royal house bestowed on his parents by Queen Elizabeth II when they got married; or Mountbatten-Windsor, the two-for-one surname of Prince Philip, who got Mountbatten for his maternal grandparents, and the queen, whose father, King George V, selected Windsor for his family in 1917.
Look how modern Philip and Elizabeth were, adopting a hyphen like that back in the day! (Fun fact: An Order of Council mandated that their descendants could start using Mountbatten-Windsor in 1960, and it's the surname used by Charles and his sister, Princess Anne.)
(Originally published June 26, 2013 @ 2:01 p.m. PT)