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).
If you mean Prince Harry (whose actual giiven first name is Henry), the son of the Prince of Wales. then his legal surname is Mountbatten-Windsor but he uses his father's (and by extension his) territorial designation, Wales, in the Army. It is common for Royals to use their territorial designation rather than their actual surname in everyday life.