Forgotten Title BL (?) mystery fantasy/romance enemis to lovers (?) novel

uh so the story (as far as i can remember) was about this guy who was like the son of a duke and a skilled magician from the black tower (?). and it starts when the duke dies and the mc (?) becomes the duke since he has no other siblings, as far as i can remember the mc was really like smart, a bit morally gray, cunning, and over all mysterious (?) like nothing much is said about him besides that hes the dukes second son. i think i remember him having an older brother that died bcs of some disease (?), the novel only mentioned the he has a twin like mids like chapter 50≈ or something i dont really remember it clearly. but um the ML (?) was like a wizard who came to like the mc's duchy to um i think it was to find out the reason for the dukes death? idk. but it was like a kinda a enemies to lovers thing w bantering and stuff, all i remember abt their relationship was that ML was really suspicious of MC in the start since he thought the he had something to do with their deaths and i think in one of the chapters the mc said something like "yeah ik they were going to die but I didnt kill them so youre wrong" oh yea and then it was revealed that the mc wasnt actually human human like he was a spirit/ghost (?) i think and it had something to do with the duchess and the twin thingy. anyways thats all i remember if you think it sounds familiar please tell me (;´༎ຶД༎ຶ`) ive been trying to look everywhere for it and i still cant find it QAQ

oh yeah and it was also more focused on power struggle/ politics in the beginning (if that helps)