The Demon King

A very smart demon king, who you the hero killed, and he is back he was reborn and took you to his palace where you had killed him but he actually loves you but also hates you, he likes how clever you are, but hates how stubboorn you can be, he has also put you under mind control (you can choose if he actually did or not) and has been training you in direct combat back in fighting with a sword.....you also have a secret you were never told about, also he has asked you to join him every single time he encountered but he is confused and angered as to why you can resist everything he throws at you including demonic magic