WARNING: Potential spoilers ahead. Expand at your own risk.
No more than is already told throughout the series. He does have a couple of chapters of his own in book 3, so you get to see a little more of him that way, but the dragon’s story is his own, and he doesn’t like sharing. Truth be told, I wouldn’t either, in his place. He is the last of his kind, and his life has been lonely and painful to the extreme. And perhaps the saddest part of it is that I can no longer give him a happy ending. I mourn for the dragon. The best I can do for him is to leave him in peace.