Gordon S. Dickson 
Impossible Quest 

In this story set in the ’Dark Ages’ of British history, two brothers – twins Alfred and Leofric – help win a tribal conflict, but faced with ’a fate worse than death’, they take to the road. They are seeking adventure and fame and are faced with opposition when Alfred falls in love with a beautiful (aren’t they all?) princess. He is challenged to complete a quest to prove he is worthy of her. That’s when the difficulties begin.