Beast, by Donna Jo Napoli. 2000.

Persian Prince Orasmyn loathes violence and dreams of love, anticipating his eventual betrothal to a suitable princess. When a ritual Islamic sacrifice goes awry at his hands, he is cursed by a parian, or fairy, and changed into a lion. After years of wandering and struggling to survive as man-within-lion, Orasmyn winds up in France, there to become the supporting actor in a dramatic recasting of "Beauty and the Beast." Orasmyn is a strong protagonist (and a convincing lion); Beast is a thoughtful retelling, at once both visceral and spiritual, and, by all indicators, well-researched. Recommended.