Books in the Heirs to Eternity series

Prince Anryn of Ammar isn't the heir his father wants. After assassins wearing the royal sigil strike at a witch trial, Anryn is on the run and desperate for help. He meets Maertyn Blackfire, a lonely witch cursed with immortality by the mages of Nynomath, Ammar's enemy. Together, they uncover a curse on Anryn that might explain why his father wants him dead: Anryn is really a woman… and a witch.