Nightbringer | The Arthurian Online Encyclopedia

Ysberin

Sberin, Ysperni

A warrior in the service of King Arthur who was the son of King Fflergant of Armorica.

He is thought by many scholars to be equal to Duke Alan Fyrgan (1084-1112). Alan married William the Conqueror’s daughter.


Source
Culhwch and Olwen | Late 11th century