The King's Heir is the third and final book in the Kingdom Fea series. 

A group of mysterious ghouls are terrorizing a remote desert town on the western side of the kingdom. Prince Osiel and his father's most trusted council members are granted the task of eliminating the nuisance. As Osiel works with his father's council to uncover the truth behind these creatures he learns more about himself and his heritage than he ever desired to know. Members from each dimension are called in to help remedy the problem, but it will come down to Oseil to stop the mad man that's behind the ghouls' creation.  Can he defeat his self doubt cause in time to gain full control of his magic abilities, or will he be to late?