Sir Lionel is the younger son of King Bors

Bors

Bors circa 540s-580s, is the name of two knights in the Arthurian legend, one the father and one the son. Bors the Elder is the King of Gaunnes or Gaul during the early period of King Arthur's reign, and is the brother of King Ban of Benoic. Gaunnes is the Fredemundian dynastic kingdom of Neustria...

 of Gaunnes (or Gaul

Gaul

Gaul was a region of Western Europe during the Iron Age and Roman era, encompassing present day France, Luxembourg and Belgium, most of Switzerland, the western part of Northern Italy, as well as the parts of the Netherlands and Germany on the left bank of the Rhine. The Gauls were the speakers of...

) and Evaine

Evaine

Evaine is a queen in Arthurian legend, the sister of Elaine, mother of Lancelot; she and her sister married brother kings and suffered parallel fates, both women losing their husbands and sons and then entering the same convent...

 and brother of Bors the Younger in Arthurian legend. He is a double cousin of Lancelot

Lancelot

Sir Lancelot du Lac is one of the Knights of the Round Table in the Arthurian legend. He is the most trusted of King Arthur's knights and plays a part in many of Arthur's victories...

 and cousin of Lancelot's younger half-brother Ector de Maris (not to be confused with the older Sir Ector, who was King Arthur's foster-father). When their father dies in battle against King Claudas

Claudas

King Claudas is a fictional Frankish king and an opponent to King Arthur, Lancelot, and Bors in Arthurian literature. His kingdom is named "Terre Deserte", or "Land Laid Waste", so called because of the destruction Uther Pendragon had wrought there. Claudas appears as the Round Table's adversary in...

, Lionel and Bors are rescued by the Lady of the Lake

Lady of the Lake

The Lady of the Lake is the name of several related characters who play parts in the Arthurian legend. These characters' roles include giving King Arthur his sword Excalibur, enchanting Merlin, and raising Lancelot after the death of his father...

 and raised in her underwater kingdom alongside her foster-son Lancelot.