User blog comment:Zippertrain85/Dawnguard Follow up./@comment-17114085-20131216013719/@comment-17114085-20140114140956

Also if he was a King in High Rock it would have to be in the 2nd Era, as in the 1st Era the province was still ruled by the Elves. Even so most, if not all, High Rock Kings were Bretons in the 2nd Era. Harkon is clearly a Nord so it's unlikely he ruled over a High Rock Kingdom.