I think he’s the new emperor that the female emperor was talking about w/ dojin and I think that’s gonna cause some problems there was also a moment in an earlier chapter where it foreshadowed it cause it was an emperor who looked sus that said something along the lines of “I can’t wait to see you dojin”
It is just my opinion but i think that mysterious king is that asshole from Dojins timeline that raped him...the one Dojin keeps having nightmares of-when Yellow Dragon asked what Dojin was most afraid of the cat said that it was that guy (the one with the eagle tattoo...do not remember the name).
I think he is the guy in his nightmare in chapter:
http://www.mangago.zone/read-manga/tale_of_the_yellow_dragon/uu/tale_of_the_yellow_dragon-chapter-5/1/
His name is Sunhoo i think
Who is that bastard with eagle tatoo.