"The Lost Years of Merlin" by T. A. Barron was the first book in the Quintilogy
In the beginning of the book, we find that a young boy has just regained consciousness, and finds he, along with a woman with long blond hair and a tattered blue tunic, are washed up on a beach. The boy encounters a boar as he is walking toward the woman, and tries to attack it. It stamps it's foot on the ground, signaling that it is going to attack. With tusks like razor blades, it charges at the boy. He tries to drag the woman into a hollowed out tree trunk. He puts the woman in first, then tries to fit himself in. A beautiful stag leaps from the forest and stands between the two. The stag and the boar fight. Angrily, the boar retreats. The stag looks at the boy with the deepest eyes the boy would ever see. The woman declares herself the boy's mother, and that her name is "Branwen", and his is "Emrys". Years later, Emrys finds that he has magical powers and eventually uses them to defend Branwen against a terrorizing bully who is trying to burn her at the stake. Tragically, he accidentally sets a tree on fire that collapses on the boy whom Emrys tries to save and fails.
Emrys, attempting to help the boy, goes blind from this incident, but learns to see through a visual "second sight", after swearing never to use his powers again. After learning to sense well enough to be mobile, Emrys leaves Branwen at the monastery where he had been treated for his burns, and sets out to find his true home.
Emrys builds a raft and floats all the way to the magical and mythical island of Fincayra, which is somewhere between heaven and earth, also called the "in between," place.
There he meets Rhiannon, a girl of the Druma, who agrees to help him find out who he truly is. He learns, from a wise Bard named Cairpre, that Branwen really was his mother, but her real name is Elen, and, to his shame, that his own father is the king: Stangmar, an evil tyrant who is trying to take over all of Fincayra. He then chooses to try and stop his father, who has caused, unknowingly, destruction to the magical realm. Emrys proves himself when he succeeds in this, with the help of Shim, a small giant, a trusty hawk, Trouble, and completing a prophecy of ancient times. Rhia tells him he should think of better name, so he then decides on Merlin, after his hawk that gave its life for him.