Anonymous. When I was 30, I had a nanny job that was at least 10 hours a day, plus I would spend up to 3 hours a day commuting, sometimes more. It almost killed me and I was tired all the time and honestly, I was not a great nanny to this family because of it.
Therefore, Mountbatten-Windsor is the surname of all male (and unmarried female) descendants of Prince Philip and Queen Elizabeth II; this includes Prince Charles, Prince William and Prince Harry. Because Prince Harry and Price William use the title Prince, they do not use the last name Mountbatten-Windsor. They use the surname Wales because they are the sons of the Prince of Wales. Although Royals don't tend to use a last name, in the instance of a marriage, for example, Prince William's last name is Mountbatten-Windsor. This is the surname of all descendants of Prince Philip and Queen Elizabeth II (excluding females who marry).
Most people probably don't even know Harry's full name: Henry Charles Albert David. And those who do, likely assume his last name is Wales, but that name really signifies the dynasty from which he hails. Being that Harry is the son of Charles, Prince of Wales, he inherited the same dynastic distinction to signify the royal house from which he hails. This is similar to his younger cousins, Princesses Eugenie and Beatrice who both use the last name York, as their father is the Duke of York.