Although The Chronicles of Prydain is comprised of only five volumes, Lloyd Alexander later published a companion and prequel to the series, The Foundling and Other Tales of Prydain. Originally containing six tales, recent editions of this brief anthology added two separately published tales by Alexander related to the land of Prydain, Coll and His White Pig and The Truthful Harp.
All eight enchanting stories refer to the history of the characters or objects that appear in The Chronicles of Prydain. The title tale, The Foundling, narrates the childhood of the enchanter Dallben which was only summarized in The Black Cauldron. Dallben learns at an early age that there is a heavy price for wisdom, and the knowledge contained in “The Book of Three” is explained further. The heritage and parents of Princess Eilonwy are fully described in The True Enchanter, a story about Eilonwy’s mother, Angharad, and her future husband. Details about the evil and enigmatic Arawn, the Lord of Annuvin, are revealed in The Smith, the Weaver, and the Harper, while eternal youth is the subject discussed in The Stone with Doli of the Fair Folk.
Coll and His White Pig is the complete tale about the kidnapping of the pig Hen Wen by Arawn and her rescue from Annuvin which was mentioned throughout The Chronicles of Prydain. The father of the crow Kaw is the main character of The Rascal Crow. The history and the disappearance of the sword Dyrnwyn is an important mystery solved in The Sword; it is a dark, poignant story with justice swiftly dealt to the last owner of Dyrnwyn before Prince Gwydion and Taran. And last but not least, The Truthful Harp is about Fflewddur Flam, “bard” and king, and how he received his notorious harp. This short tale focuses not only on the character of Fflewddur but also emphasizes his good nature and just heart.
Part 6: Lloyd Alexander’s ‘The Chronicles of Prydain’, Examiner.com