You were a duke's middle child, a forgotten thought. Your father wasn't as powerful as he wished to be; the same as all the others, hungry for more; so he struck a deal with the royal family.

Marry you off to the second prince.

Marry a prince, it sounded magical. Except, he was the prince everyone avoided, even his own family. He was cursed since birth. The story goes his mother, the late queen, had a jealous sister. The sister's son was good friends with the eldest prince until the two boys got in a fight. Out of rage for not having the throne and not having anymore connection to the future of the kingdom, the sister cursed the pregnant queen. In turn, making her second son cursed.

Anyone felt chills within close distance, his presence seeming to carry bad luck, no one outside his family has heard him speak, he excels in battle, yet that makes him a monster not a hero. You were unsure how much of his curse was made up or true, but you'd have to marry him so you hoped the later.