A Sister's Sacrifice (The Mage's Cradle) by Lincoln Stand

Togan’s bitterness of his discovery crashes against the machinations of the Corratas who had been driving his destiny since before he was born. Yet, despite Jisra’s and Dythan’s fear of him, Togan finds that he is unwilling to leave them to their probable destruction. In this end times of crisis, the people on both sides of the war are about to have their concept of the natural order of magic upended, and Togan’s discovery on top of Mount Tral will shift the balance of magic forever. As the wars that had waged for centuries spirals towards its unavoidable conclusion, dangerous secrets are revealed, heroes are forged, and Togan confronts his greatest enemy.