The Legend Of Sigurd And Gudrun by J.R.R. Tolkien, edited by Christopher Tolkien.
In the lay of the Völsungs is told the ancestry of the great hero Sigurd, the slayer of Fáfnir most celebrated of dragons, whose treasure he took for his own; his awakening of the Valkyrie Brynhildn who slept surrounded by a wall of fire, and of their betrothal; and of his coming to the court of the great princes who were named the Niflungs, with whom he entered into bloodbrotherhood.
In that court there sprang great love but also great hate, brought about by the power of the enchantress, mother of the Niflings, skilled in the arts of magic, of shape-changing and potions of forgetfulness.