God of the Sun (Wine of the Gods Series Book 29)

Warric Menchuro is a Prince Primus of Arbolia. The product of his mother's rape by an insane "god", once he reaches the age of twelve, he'll be adopted as a son of the Emperor and educated to become a useful part of the government. So long as they don't discover that he can do magic. Because the Priests control all magic, and they're always delighted to find a magician to turn into one of their chained and enslaved gods.