Which 1969 Newbery Medal winner concludes Lloyd Alexander's Prydain series?

The High King is the 1969 Newbery Medal winner that concludes Lloyd Alexander’s Chronicles of Prydain.

Published in 1968, the fantasy novel is the fifth and final volume of the series. It brings Taran, once an impulsive Assistant Pig-Keeper, into the decisive struggle against Arawn and forces him to weigh personal desire against responsibility to Prydain. The story completes his maturation and his path toward becoming High King.

The award year follows the Newbery’s standard convention: the book appeared in 1968, but the medal was awarded in 1969. The series draws heavily on Welsh mythology and folklore, although Prydain is Alexander’s own fictional kingdom.

The other choices belong earlier in the sequence. The Book of Three opens the series, The Black Cauldron is the second volume and a Newbery Honor book, and Taran Wanderer is the fourth. The High King is the medal winner and the concluding installment.