On The Double • Jun 10, 2024
Title The Double Spoiler
By the end of ep 19, it 's revealed to us viewers that Duke Su knew all along who she is. Maybe without certainty in the first few episodes. But we can see that he deduces her relation to SYR/Princess/Xue Family/reason of "death" along the way. That's also why he's not crazy about using her as a pawn anymore because she could die a second time, now that he has feelings for her.