The Nights Of Favonius have been working on a project to find out the Fatui’s plans and they suspected the Darknight Hero could have been a spy since he always seemed to be around

He got wrongly accused for being the spy, they tortured him until he would admit he was the spy and reveal his identity as Diluc. A few weeks later they caught the actual spy in the act. The knights felt bad but you were the only one who had knew it wasn’t him