I think the reason King Theodore asked her to kill him was because he started showing signs of the curse(?) and he needed someone to kill him so he wouldn't go berserk and attack someone. This causes the FL to run out of the room, accusing him of not loving her. She has to be the one to kill him, though, or else someone else would get the authority to the throne, so he accuses her of treason, I think it was?? so that she really has no choice but to kill him. He may have reincarnated into the current ML -or- the current ML is his descendant. I kinda doubt the descendant part because the FL noted that this was the house of the loyal knight.