Fugitive Prince: The Wars of Light and Shadow (Third Part) (Alliance of Light/Janny Wurts, 1st Bk)

Two half brothers, cursed by a Mistwraith to a lifelong enmity, whose gifts of light and shadow are set into violent conflict:
Lysaer, Prince of the Light. A dedicated, charismatic leader, sworn to uphold justice and set humanity free from the Sorcerer's rule, he will claim Divine Power to safeguard his people from an enemy he firmly believes will destroy them.
Arithon, Master of Shadow. Brought up a trained mage, given a musical talent that has won him the title of Masterbard, he wishes for nothing but to defuse war and strife, and search out the vanished old races, whose grace holds the key to the world's fragmented peace.
With the appalling destruction of the Vastmark warhost, recoil and grief reshapes the balance of power in the Five Kingdoms. Koriani enchantresses join forces with Lysaer in a desperate bid for power, and their intrigues threaten Arithon's hard-won autonomy. The aging Koriani Prime Matriarch wants the Shadow Master taken captive, no matter what the cost - or the means. For his life stands as her bargaining chip to break the deadlocked rivalry with the Fellowship Sorcerers.