Tysilio/Tysilius(/Suliac). Brut Tysilio (History of Tysilio), version of Brut y Brenhinedd (Chronicle of the Kings). c Fourteenth/Fifteenth century AD (Seventh Century AD):

‘Brut Tysillo, also called the “Ystorya Brenhined y Brytanyeit” (Jesus MS. LXI)’ at Mary Jones.
https://www.maryjones.us/ctexts/tysillo.html