I am looking to identify a stand alone book where a prince battled demons in his land and castle. He lost an eye and became an axeman. I read this book in the mid to late 1990s. It got me into sci-fi.
I believe the antagonist was actually a wizard who was helping the prince (or so he thought)/prince's mentor/friend. The prince was a swordsman and lost an eye fighting demons, then took up axe as it needed less skill and depth perception.
I can't remember the names of any character though!