... Anna, sister of Arthur, is said to have married Llew, brother of Urien of Rheged, and to have had by him two sons, of whom Medrawd was one.  The other son is called, by Geoffrey of Monmouth, Walganus.  Geoffrey represents him as the faithful soldier of his uncle, under whom he fought against his own brother Medrawd, and fell in a battle which took place, according to Geoffrey, at Richborough in Kent, on Arthur's return to Britain... (The Biographical Dictionary of the Society for the Diffusion of Useful Knowledge, 1844)