Aldroen, Adroenus, Aldroein, Audrien
King of Brittany two generations before Arthur.
When the Archbishop Guethelin, Aldroen’s kinsman, came to Brittany to beg for Aldroen’s help in driving the Picts and Huns from Britain, Aldroen sent his brother Constantine, Arthur’s grandfather, to accomplish the task and assume the throne of the island.
Sources
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Roman de Brut | Wace, c. 1155
Brut | Layamon, late 12th century to mid-13th century