They use Windsor. It should really be Mountbatten as the duke of Edinburgh's last name is Mountbatten.
Prince Mountbatten
Windsor is their surname. Their titles will be Prince and Princess of Wales.
His father is HRH The Prince of Wales, so Prince William takes the surname 'Wales'The Royal Family don't tend to use surnames unless one is required by custom, in which case a surname is used based on the person's title or family.Prince William can use the surname 'Wales' (due to his parents being the Prince and Princess of Wales) or 'Cambridge' (as he is the duke of Cambridge) or 'Mountbatten-Windsor' (which is his family name).
William Wales
Mountbatten-Windsor but he uses the surname Wales in his professional life.wales
The surname of the current royal is Mountbatten-Windsor (hence, the Lady Louise Mountbatten-Windsor, is the granddaughter of the Queen and daughter of her youngest son, Prince Edward). In 1960, just before the birth of Prince Andrew that same year, the Queen drafted up an order saying that her children, grandchildren, and other descendants will carry on this surname. It is a hybrid of Mountbatten (Duke of Edinburgh's surname) as well as the Queen's surname (Windsor). Technically, officially the royals use whatever title they have as a surname (I.e. Princesses Beatrice and Eugenie use York as their father Prince Andrew is the Duke of York and Princes William and Harry use Wales as their father is the Prince of Wales and as such has this has this as a title---AKA William Wales, Henry Wales which is what they use in the military that they are currently serving in respectively).
After marrying Prince Charles she became Her Royal Highness The Duchess of Cornwall
Their surname is Windsor- some people use 'Wales' as their surname because Prince Charles is the Prince of Wales, although this is incorrect and creates anger & resentment amongst Welsh people, since neither Charles, William or Harry ever go to Wales or have the slightest interest in the place.
Mountbatten-Windsor but he uses the surname Wales in his professional life.wales
Prince William has various surnames available to him, including 'Wales', 'Cambridge' and 'Mountbatten-Windsor'. The surname a royal uses (if they use one at all) tends to reflect their title.
His full name is:Charles Philip Arthur George
Prince Henry doesn't need a surname, but it would be Mountbatten-Windsor. His full name is Henry Charles Albert David. Note that his brother, Prince William, adopted the surname Wales whilst attending university.
Prince Williams adopted the surname Wales whilst at college, so their surname would be Wales. However, the Queen conferred upon them the titles of The Duke and Duchess of Cambridge, so that will be the names by which they will be known, until the current profile of the Royals changes.