The Ducal Family's Poisonous Flower summary:

Lily Roland, the daughter of Duke Roland, stumbled upon her fiancé and her illegitimate sister having an affair! She was poisoned by the two people whom she grew up with, and thrown into the wilderness.When her life was hanging by a thread, she was saved by a monstrous creature that had a body of a human, but a head of a beast, who turned out to be the Crown Prince, Isaac Stewart.Isaac was cursed by a mysterious witch to turn into a bloodthirsty monster on the night when the moon is full, and Lily’s blood is his only antidote!Isaac decides to help Lily in her revenge, but in exchange, she must marry him and assist him in lifting the curse.