The HRB IX 11 tells us Gwalchmai, referred to as Gualguainus son of Loth, was twelve years old and had been knighted by pope Sulpicius. If this is a reference to the papacy of Simplicius (468-483) then it suggests Gwalchmai was likely of gen. -1. This dating is confirmed by a piece of inforamtion by William of Malmesbury, despite the fact he wrongly believes Gwalchmai was a nephew of Arthur:
“Regnavit in ea parte Britanniæ quae adhuc Walweitha vocatur: miles virtute nominatissimus, sed a fratre et nepote Hengistii … Cæterum, alterius bustum, ut præmisi, tempore Willelmi regis repertum est super oram maris, quatuordecim pedes longum …”
“He [Walwen] reigned in that part of Britain [Ros in the province of Wales] which is still called Walweitha. A warrior most renowned for his valour, he was expelled from his kingdom by the brother and nephew of Hengist … The tomb of the other [that is Walwen], however, as I have said, was found in the time of king William upon the sea-shore, fourteen feet in length …”
This would be compatible with HRB IX 9 which states Loth had married in the time of Aurelius Ambrosius. It follows that Loth would have been of gen. -2. That name appears in the ByB fol. 81 as “lew vab kynvarch”, that is Llew ap Cynfarch.. Bromwich explains:
“Considerable confusion prevails in Welsh sources owing to the fact that Geoffrey of Monmouth gives Arthur’s sister Anna as the mother of Gualguanus. In the fourteenth-century Birth of Arthur (Cy. XXIV, pp. 250 ff.) an attempt is made to reconcile the native tradition with that of Geoffrey by substituting the name Gwyar for that of Anna as Arthur’s sister …”
In its bid to reconcile contradictory traditions, it incorrectly maintains Gwyar was the daughter of Gwrlais and Eigr. However, it correctly says that Gwyar was first married to Emyr Llydaw and then to Llew ap Cynfarch. This explains the reference to Aurelius Ambrosius in HRB IX 9, mentioned above, as Emyr Llydaw is likely to be a title held by him. Emyr Llydaw was of gen. -2, see table below, as indeed was Llew, see above.
|Gen.||ByS J 21||Proposed pedigree|
 Hardy, T. D., 1840 vol. 2, 466.
 Chambers, E. K., 1927, 17.
 Parry, J.J., 1937.
 Bromwich, R., 2006, 369.