Dark Ones Take It

Werewolves as you've never read them before.

Caedon and Maeldoi are brothers. And they are gwrgi--creatures who look like the rest of us, except for their amber eyes. When they get into a rage, they transform. To wolves? Not exactly. To an out-of-control bestial form of themselves. As the brothers reach young manhood, the dangerous age, they are separated. Caedon is adopted by Gilles de Rais, a powerful mage with powerful secrets, a sorcerer who values Caedon's rage and schemes how to use it. Maeldoi is taken off by his fellow gwrgi to be taught how to control the rage inside him. When they meet again, the fate of the Spheres themselves hangs in the balance.

The origin story of the villain of the Stormclouds/Harbingers fantasy novels.