This is the fourth book in The Chronicles of Prydain.

Description from Goodreads
Taran is an Assistant Pig-Keeper no longer; he has become a hero. Now he dreams of winning the hand of the Princess Eilonwy. Eager to find his origins, Taran sets off with the faithful Gurgi on a quest across the marvelous land of Prydain. Their journey takes them to the three witches in the Marshes of Morva, through the many realms of Prydain, and finally to the mystical Mirror of Llunet, which may hold a truth about Taran's identity that he cannot bear to face. In the course of his travels, Taran will learn much about his world and the good and bad people in it, but will also discover much about himself.

Received today.

I'm looking forward to reading this series, as I love all things magical and mystical.