Kustenhin Vendigeit (Constantine the Blessed; Custennin Gorneu ["the Cornish"]). Bromwich* equates the Cornish Custennin (who appears in the same position in a related genealogy in the Bonedd y Saint ["Pedigrees of the Saints"]) with the 6th C. prince who is one of Gildas' targets in De excidio Britann(i)ae (see Other Works) and notes that this may be the same person who's conversion is noted in the Annales Cambriae for the year 589CE (see Other Works) and therehence the saintly King Constantine of the Life of St. David (c.512–587). However, the name was obviously popular from the rule of Roman emperor Constantine the Great onwards, or, more probably, the rule of Constantine the usurper, who was proclaimed emperor by troops in Britain in 407 CE. Bromwich* lists at least three additional Constantines that may have existed. The proliferation of Constantines has caused much confusion, not least because Geoffrey of Monmouth's Historia Regum Britanniae (see Other Works) mixes up at least the emperors, if not all of the Constantines, with repeats*.

Geoffrey gives Constantine, grandfather of Arthur, three children: Constans (in line with both emperors), given in the Triads as Custennin Vychan ("the little"*); Aurelius Ambrosius (known in the Welsh sources as Emrys Wledic); and Uthur Pendragon. This certainly seems like an attempt to shovel as much into the family story as possible on Geoffrey's behalf. Other Welsh sources give him a child, Erbin, the father of the pre-Arthurian(?)/Arthurian hero Gereint*.

Bromwich* additionally suggests that the characters of Custennin the Shepherd and his son Goreu (listed as a cousin of Arthur) from the Welsh tale Culhwch ac Olwen (Summary) are a misreading of Custennin Gorneu. As she notes, this does suggests some kind of link for Custennin with an Arthurian literature which seems pre-Geoffrey, although a rather slim one. Goreu also appears in (the albeit post-Geoffrey) Triad 52 as the cousin of Arthur via his mother and Amlawd Wledig*.