Who was King Vortigern's predecessor?


I seem to remember reading about Vortigern’s predecessor many years ago. I have not been able to find anything on Google regarding any kings before Vortigern. From what I remember of this figure (however mythical) Vortigern schemed to succeed him as king. I don’t remember the details. I hope someone can help me. I look forward to your feedback.

The one I know is Constantine (III or II, depending on if counting as Western Roman or British), the father of Uther Pendragon and Ambrosius Aurelianus. That’s according to the*Historia Regum* of Geoffrey of Monmouth. Or perhaps you’re thinking of their brother Constans.

The other figure associated with him is the historical Magnus Maximus, whose( otherwise unattested )daughter was supposedly Vortigern’s wife. This is based on a 9th century Welsh inscription tracing a royal ancestry, so again firmly in the realm of the legendary.

Right… I always had the impression that after the Romans pulled out, you had a sort of gradual decline where the Romano-British fragmented into multiple smaller kingdoms, and Vortigern was one of those kings, and happened to get lucky enough to get mentioned by Bede.