This scene from the preview trailer caught my attention. It gives us a glimpse of a man's tortured soul. Who could that be?!
Rough translation by Milawaty [YT] :
Haseon: I know that if I want to bear this position (as a king) I should feel this kind of hurt
Lee Kyu: How couldn't you keep to stay silent till the end?
Haseon: As you have said, to live at this palace there are only two ways..
Chi soo: kneel down! I will tell you the way to save your younger sister..
Haseon: Do you want to resist till the end?
Chi soo: Now call the sinner court secretary right away! Then I will declare your sister as the court lady!
Haseon: Now only one way left I could take...