Nice concept, mate!
My suggestion might be to introduce two characters: one being the antagonist, one being the mentor, and the reveal be the fact that they are the same person. Maybe drop subtle clues throughout the story such as unexplained disappearances (gaps in his attendance in the story where he would have been expected to be there), perhaps him being fiercely defensive of a certain philosophy; just little moments where he drops his facade that gives the audience (and the protagonist, if you wish to go that route) clues.
Happy writing! Looking forward to seeing some more ideas about the world and the story
until