Two entries with the name Borel.
Borel
Berell, Berille, Bretel, Bretelot, Dorell
Arthur’s cousin or nephew, upon whom Arthur bestowed the rulership of Maine or Le Mans.
He fought for Arthur in the war against Lucius the Roman, and accompanied a prisoner train through France. The prisoner train was attacked by the Romans, and Borel was slain by King Evander of Syria in the battle.
Sources
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Roman de Brut | Wace, c. 1155
Brut | Layamon, late 12th century to mid-13th century
Prose Brut | Late 13th century to late 15th century
Alliterative Morte Arthure | c. 1400
Le Morte Darthur | Sir Thomas Malory, 1469-1470
Borel
A Saxon early killed by Arthur at the battle of Bath with his lance, Ron.
Source
Brut | Layamon, late 12th century to mid-13th century