Like Charles said, lots of parents give their children royal titles as names. In addition to all the names meaning "King" he cited, there's Cesar Romero, from Caesar, the Roman imperial title that spawned the titles Kaiser and Czar. In my Tangent Knights audiobook trilogy, the second female lead is named Malika, which means Queen in Arabic. And so on.
In addition, some parents even give their children fictional royal titles as names. Remember all the parents who named their daughter "Khaleesi"? I wonder how that's working out for them now...
