Lord of Midnight by Jo Beverley

The same rebellion that leaves Clarence of Summerbourne dead also leaves his castle and his daughter, Claire, forfeit to the king’s champion. Renald de Lisle arrives at the castle gates as a warrior, takes possession of Claire like a conqueror, and sets her heart racing as her lover. Amid moonlight and velvet, she becomes his bride; atop tangled bedclothes she discovers passion. But then she learns Renald’s terrible secret and vows revenge against this man she wed, this man she loved with all her heart.