The Moon Lord — Terri Lynn Wilhelm

LORDS OF MIDNIGHT
In an age of danger and tyranny, the fight for a woman's heart can become the most passionate battle of all....

To all of England, the fearless warrior known as the Moon Lord is a legend. To Rosamund Bourton, the mistress of Wynnsef, he is more. An imposing figure in black armor, Tancred de Vierzon has arrived at the gates of her family estate as its new master. It is his just reward for service to King Richard the Lionhearted -- and his revenge for the shocking betrayal of a fellow crusader: Rosamund's own brother.

But as the mysterious de Vierzon takes command of the castle, so does he conquer a permanent place in Rosamund's heart. Now, torn between family loyalty and human desire, Rosamund must make a choice that could change her destiny forever....