Pride — Frances Stockton

They have lived for centuries. An ancient, secretive race of were-panthers faced with near extinction. To assure their survival they must conceal their identities and abilities, while protecting mankind from an unimaginable, primordial evil.
Pride: The Abcynians, Book II
Plagued by headaches and memory loss after a life-threatening injury, Rhiannon has spent years confined behind the walls of a decrepit castle. When a loathsome earl attempts to earn her favor with an extravagant painting, she is inexplicably drawn to its depiction of an ancient, mythical race. Believing the Florentine artist could be the key to unlocking her past, she and her maid escape, hoping to enlist his aid. Upon reaching the Piazza della Signoria months later, she is unaware that the handsomest man amongst the lavish merchants is the one she seeks.
Dante Luciano is considered the most renowned artist of his time. His patrons are wealthy and powerful. His charm and prowess with women legendary. Yet, as the adopted son of the king of his kind, he must guard his secrets. For he possesses the heart and soul of a panthera prince, therefore, able to shift into a lion. Taken by the discovery of a rare Abcynian female nearby, he recognizes her as his destined mate. Discovering Rhiannon is stricken with debilitating pain, he takes her home, providing the remedies, protection, and knowledge she needs to survive.
While she heals, they fall in love, beginning to plan a future together. However, when her memory returns, imminent danger looms. It'll take all of Dante's abilities and the Abcynians to save Rhiannon from a vicious, beastly foe.