@Sheep It was so that he would not try to conquer Earth basically, if he was just a king from another world it is doubtful he would respect Earth culture, and decide he can rule it better than the Earthlings can, with the sheer level of pride he has. The real reason is that the most bad a*s guy had to be from Korea of course according to the Author.
Read Cursed Princess Club, it's finished and fantastic.