Merthur - The Blue Butterfly
When Uther Pendragon finally tracks down the rogue dragonlord to Ealdor he finds the man with a wife and child. The king feels no guilt when he enters the couple's home, killing both Balinor and Hunith as they try desperately to protect their son. But, instead of having the child meet the same fate Uther decides to keep the young dragonlord as a form of token. A spoil of war. So, once he returns he locks the boy away somewhere deep in Camelot's dungeons.
Merlin remains there for years, alone and afraid until one day a young prince finds him.