Britu is a son or descendant of Vortigern in various medieval Welsh genealogies.
In Jesus College MS. 20 Genealogies, section 16, Britu (Bredoe) is son of Cadell Ddyrnllwg, son of Catigern (Cedehern), son of Vortigern. He is father of Thewer, father of Cassanauth, father of Kynan.
In Bonedd y Saint section 62, ABT 6k, ABT 20, and Hen Lwythau, Britu (Brutus, Brydw, Bridw) is son of Rhuddfedel, son of Catigern (Kynderyn), son of Vortigern. In Bonedd y Saint, section 62, Britu is father of Cadell Ddyrnllwg, father of Kyngen, father of Brochfael. The other genealogies make him father of Pasken, father of Cadell Ddyrnllwg, father of Kyngen, father of Brochfael.