Geoffrey's Cligueillus / Digueillus may be a corruption of the Old Welsh name Higuel (specifically, the 10th century AD king Higuel (Howel/Houuel) Bonus - i.e. Hywel Dda - mentioned in one of Geoffrey's sources, the Annales Cambriae, now Modern Welsh Howell.
Annales School | Annales Fuldenses | Annales | Annales Laureshamenses | Annales de la Société Entomologique de France | Annales Cambriae |