Lord of Hearts by Mary Gillgannon

A Welsh princess. An English knight. They met and wed as enemies. Found passion as lovers. And must become allies to survive.
When Marared’s chieftain father decides to marry her off to Gerard of Malmsbury, she is furious and vows to thwart her father’s plan of forming an alliance with the hated English. Gerard is shocked by his bride’s fiery, combative nature, but also determined to hold on to his rich prize. Not only does the marriage secure his hold on Tangwyl Castle, it elevates him to the status of baron, an unlikely honor for a man born a bastard.

Gerard hopes to win over his hostile new wife with kindness and consideration, but Marared does not give in easily. Even as the attraction between them builds to shimmering passion, she stubbornly continues to plot to end the marriage. Gradually Marared comes to realize that Gerard is her love and her destiny, but it may be too late. Her scheming has entangled them both in deadly Welsh politics. Not only does it appear their marriage is doomed, but both their lives are in peril.