AI character Class Default's won't allow me to set my own AI Controller Class

Hello! I’ve been working on a school project on a game that has a character that patrols and searches for the player character. To do this I am using a behavior tree. I have created an AI Controller class called “AI_Control”. When going into my AI character’s blueprint, which is a duplicate of the “Third Person Character” blueprint I am trying to change within the Class Defaults > Pawn > AI Controller Class to “AI_Control”, but it refuses and just says “None”. Any AI Controller Class that I have made has done this. Please help me set it to “AI_Control”.