According to royal historian Marlene Koenig, the third baby’s official title is His Royal Highness Prince [name] of the United Kingdom of Great Britain and Northern Ireland. But not so fast. Since Prince William and Kate Middleton are technically the Duke and Duchess of Cambridge, the little one will be addressed as His Royal Highness Prince [name] of Cambridge. “Royal children are ‘styled’ differently if they are the children of a royal duke,” Marlene explained of the subtle title differences to Town & Country.
Why You Should Stop Calling Kate Middleton “Princess Catherine”