According to some genealogies, Seisyll and his son were associated with Rhuddlan, perhaps as lords of its commote in Rhos cantref.
Llywelyn the Last | Gruffydd ap Llywelyn | Seisyll | Llywelyn the Great | Llywelyn | Morgan Llywelyn | Madog ap Llywelyn | Llywelyn the Elder ap Maredudd ap Cynan ab Owain Gwynedd | Llywelyn Siôn | Llywelyn Bren | Llywelyn ap Dafydd |