Tysilio/Tysilius(/Suliac). Brut Tysilio (History of Tysilio), also known as Ystorya/Historya Brenhined y Brytanyeit (History/Chronicle of Kings of the Britons). Fourteenth/Fifteenth/Sixteenth century AD (AD 1695):

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