Is this the same piece as "Merlin"
Le Morte d'Arthur was written by Sir Thomas Mallory in a set of 8 books. When William Caxton published it in 1485 it was expanded into a 21 volume set. These books chronicle the life, loves, and death of Arthur. Starting with his birth—the result of a rape on Igraine by King Uther, through his coronation, retrieving Ex-Calibur from the rock, his love and marriage to Guinevere, and ending with the battle in which he kills his son Morded and dies himself. Merlin is featured prominently in many of the stories, and his imprisonment is the subject of book 4, however, “Merlin” and Le Morte d'Arthur would not be considered the same thing.
Enotes has some more resources for this topic.