The Cavalier's Woman — Joan Hunter

Rupert, The Devil Prince He was a hot-tempered, arrogant Cavalier, the most favored of the king's generals, a brilliant tactician and a royal prince. His love seemed far beyond Venetia's reach. Yet she knew from the first moment she saw him that he must be hers--and hers alone. Bloody civil war, political intrigue, and jealous hatred separated them and kept them from happiness, but Venetia would risk anything--her family, her honor, even her life--to be his lover. She was ready to follow him to hell itself. This was originally published as two separate volumes, Rupert the Devil and Cavalier by Hunter under the author's name of Jeanne Montague. Goodreads