Despite all of Prince Philip and Queen Elizabeth's children, grandchildren and great-grandchildren all historically sharing the surname Mountbatten-Windsor, it is most likely Harry and Meghan's children with adopt the surname Sussex.
When William and Harry were at school, they were known as William and Harry Wales — a consequence of their dad being Prince Charles of Wales.
Similarly, George, Charlotte and Louis are known as the Cambridges, referring to their parents titles as the Duke and Duchess of Cambridge.
It’s thought the decision was made to help the royal children blend into their school environment, while also neatly tying in with their parents’ titles.
The royal family is still known wholly as the House of Windsor, but when Queen Elizabeth II came to power, she made the slight modification to Mountbatten-Windsor, in a nod to her husband’s adopted surname.