Llefelys
The tale appears in the Red Book of Hergest and the White Book of Rhydderch , the source texts for the "Mabinogion" , and embedded into various versions of the "Brut y Brenhinedd" , the Welsh adaptation of Geoffrey of Monmouth's "Historia Regum Britanniae" . 
<triplet> Red Book of Hergest <subj> Historia Regum Britanniae <obj> has part <triplet> White Book of Rhydderch <subj> Mabinogion <obj> edition or translation of <triplet> Brut y Brenhinedd <subj> Historia Regum Britanniae <obj> edition or translation of <triplet> Geoffrey of Monmouth <subj> Historia Regum Britanniae <obj> notable work <triplet> Historia Regum Britanniae <subj> Geoffrey of Monmouth <obj> author