The Golden Swan — Nancy Springer

A Wondrous Quest Through Lands of Magic And Enchantment, an epic adventure soaring to fantastic new worlds through the splendor of loyalty and love. Young Dair, changeling son to King Trevyn of Isle, is called by a mysterious vision to share his destiny with a strange wandering youth know as Frain. But when the gentle wolf-human Dair finds his bond brother, the curse of a dark enchantment and the search for a lost love has claimed Frains injured heart. Now Dair must journey with him, for only together would they unveil the prophecy and know the peace hidden with their web of fate.