A twelfth-century pseudo-historical count of Brittany found in Etienne de Rouen’s Draco Normannicus.
Henry II of England was conquering Rollandus’s kingdom, so Rollandus sent to Arthur, who was living in a southern paradise, for assistance. Arthur, in turn, sent a message to Henry warning him to leave Brittany alone and to prepare for Arthur’s return. Henry ignored the message and Arthur never appeared.
Source
Draco Normannicus | Étienne de Rouen, c. 1169