Prince Harry and Meghan Markle change the last names of their children Archie and Lilibet. While their last name would logically have been Mountbatten-Windsor like other members of the royal family, Harr's children now use Sussex.
The couple made the decision a few months ago to "unify" their family, now using the last name Sussex for their two children. This decision is anything but trivial and marks a break with current tradition: members of royal family who do not bear royal titles and are linked to the family by a male descendant have since 1960 all had the same surname.