What’s in a royal last name?
Prince WilliamandPrince Harrymay be brothers, but their children probably won’t share a surname.
WhenPrince Georgestarted school, it was announced that he wouldn’t be known as “His Royal Highness” in the classroom. Instead, he’ll use his father’s title as the Duke of Cambridge (momKate Middletonis known as the Duchess of Cambridge) and beGeorge Cambridgein school records and to his peers and teachers.
Since Harry andMeghan Marklereceived thetitles of Duke and Duchess of Sussexupon their marriage, it makes sense to assume that their children – starting with theirnewborn son– continue with the tradition and will likely use “Sussex” as their moniker.
Prince Harry, Meghan Markle, Kate Middleton and Prince William.Chris Jackson - WPA Pool/Getty

Bestowing titles to members of the royal family on their wedding day is a longtime tradition. WhenPrince Andrewand Sarah “Fergie” Ferguson tied the knot, the Queen made them the Duke and Duchess of York (the title that once belonged tothe Queen’s own fatherbefore he became King George VI.) It’s not always dukedoms that she hands out: WhenPrince Edwardmarried Sophie Rhys-Jones in 1999, they became the Earl and Countess of Wessex.
Richard Pohle/The Times/PA Wire

The addition ofPrince Philipto the family brought about another name change, this one, the addition of Mountbatten, the last name he adopted after giving up his title of Prince of Greece and Denmark. The name belongs to his maternal grandparents — it’s the English translation of their German name, Battenberg. The change took sometime to make its way into the royal family — 1960, to be exact, 13 years after Philip married thethen-Princess Elizabeth, and eight years after she became Queen. However, this didn’t change the name of the House of Windsor, but rather just the surnames that those in said house would use when they weren’t using the style of His or Her Royal Highness (or if they’re members of the family but don’t get said style).
source: people.com