He was adopted when the winter was growing deep and cold. Irdi and Misty agreed to care for him, as practice for when Misty's pups were born. Being young wolves, the experience caring for an older pup would be good for them.
Time passed and one day the Fae came - strange pools of magic were left in the forest. When he was a young wolf, Winterheart wandered into one and was drastically changed. Ever after she followed the new Leader as his devoted mate.
Even the Elders aren't sure what happaned.