Half a King by Joe Abercrombie
Synopsis from GoodReads:
Betrayed by his family and left for dead, Prince Yarvi, reluctant heir to a divided kingdom, has vowed to reclaim a throne he never wanted.
But first he must survive cruelty, chains and the bitter waters of the Shattered Sea itself – all with only one good hand. Born a weakling in the eyes of a hard, cold world, he cannot grip a shield or swing an axe, so he has sharpened his mind to a deadly edge.
Gathering a strange fellowship of the outcast, he finds they can help him more than any noble could. Even so, Yarvi’s path may end as it began – in twists, traps and tragedy…