I once picked up a book in a bargain bin in the mid to late eighties, which I'd like to find again.
The story starts with a twin baby being stolen by evil creatures. A particular detail that sticks with me is that they fed him the breast of his nursemaid and the milk in it got him to like the taste of blood/raw human flesh (obviously paraphrasing here).
It then jumps ahead in time and the twins have grown up, one with the evil beings (demons? monsters?) and the other as a prince. He is highly trained in swordplay and much is made of different named forms (think Rand in Robert Jordan). I'm pretty sure he had an experienced and wise trainer.
The lost brother returns I think and there is where it gets really hazy. I do remember that it must have been the start of a set because it ended on a bit of a cliffhanger I think.
I'm feeling a blue cover, guy with a sword... maybe on an outcrop of rock or battlement? Bad thing approaching?
Well that's my memory of almost 30 years ago! Does anyone know which book or perhaps even series this might be?