in the Lancelot-Grail:
   The Old French Arthurian Vulgate and Post-Vulgate in Translation; Norris J Lacy, Editor; Garland Publishing
   The Story of Merlin, Chapter 8 (Vol I, pg. 235 in Lacy's Lancelot-Grail) "So they [Arthur, Merlin, Ulfin, etc.] stayed together, gladdened and finding solace in their companionship, until mid-Lent. And it happened that King Arthur, following Merlin's advice, became friends with a maiden, the most beautiful ever born. Her name was Lisanor, and she was the daughter of Earl Sevain, and she was born at the castle called Quimper-Corentin.
   "This maiden came to swear fealty to King Arthur, and other barons came with her, because they feared that he might take their lands away, so they came to him of their own free will. And as soon as King Arthur saw the maiden, he liked her very much, and, thanks to Merlin, he could at last talk to her alone, and they lay together all night. There Loholt was conceived: he was later a good knight and a companion of the Round Table. When it was mid-Lent, the king took leave of the young lady and got ready to go to into the kingdom of Carmelide along with a body of forty knights."
   Loholt is mentioned later in a description of Sir Kay, Arthur's foster- brother, who was rescuing Arthur from an ambush laid by King Lot. The text makes mention of Kay's personality, then says:
   "Nor in his life did he ever do but one unlawful thing, that is, against Loholt, King Arthur's son, whom he killed in the Perilous Forest, and he was accused in court by Perceval the Welshman, who had been told about it by a hermit who saw him slay him."

   in Lancelot, Part I, Chapter 27 (Vol II, pg. 84 in Lacy's Lancelot-Grail)
   Mention was made of those held in the dungeons of Dolorous Garde by Brandin (Brian) of the Isles:
   "...and Loholt, the son whom King Arthur had begot with the beautiful damsel Lisanor before marrying the queen and who became sick to death in this place..."
   As for Loholt, he is rescued by Lancelot shortly after (Chapter 29, pg. 86), though he remained ill for a while, so we may assume Loholt recovers from this only to die at Kay's hand... But how?

   in "The High History of the Holy Grail" or "Perlesvaus":
   from a translation by Nigel Bryant; published by DS Brewer, Rowan & Littlefield.
   In this book, a long passage (pg. 173-175) remarks on how a maiden came to Arthur's court at Pentecost with a great jeweled box. She said that within it was the head of a knight, which could only be opened by the knight who killed him. She bid Arthur try all of his knights to open it, and to grant the killer a truce of forty days after he returned from seeking the Grail. Inside the box were sealed letters that would let Arthur know the truth of the matter.
   Knights who were innocent could not open the coffer; instead, it was covered in sweat, as if someone poured water on it. Arthur tried it first, then Gawaine, and then Lancelot. Kay finally came along, as he had been busy serving dinner, and complained Arthur didn't call him to try his hand at it sooner. He obviously hadn't heard the explanation!
   In the Perlesvaus, Kay kept boasting he was as good as any knight in Arthur's court, and was indeed jealous that Arthur didn't honor him the same way he honored Gawaine and Lancelot.
   As soon as Kay tried it, it opened, revealing a sweet fragrance and the head of a knight within. Kay continued to prattle on that Arthur should be grateful now that he would know who had been killed.
   "The king sat down beside the queen and called for a chaplain of his, and commanded him to read out to everyone what the letters said. But when he had examined them he began to sigh, and then said to the king:
   "'Listen sire, and listen, my queen and all our company: these letters say that the knight whose head lies in this coffer was named Loholt, and was the son of King Arthur and Queen Guinevere. One day he courageously killed Logrin the giant. Sir Kay the seneschal passed that way and found Loholt asleep on top of Logrin, for it was his custom to sleep on top of any man he killed. Sir Kay beheaded Loholt and left the head and body there; then he took the head of the giant and carried it to King Arthur's court, and gave the king and the queen and all the knights to believe he had killed him. But these letters bear witness that he did not; it was Loholt who killed the giant, and Kay killed Loholt, by the testimony of these letters.'"
   Guinevere then fell in a swoon upon the coffer, and confirmed it was Loholt by a scar upon his face, which he had since childhood. Sir Kay slipped away, and became a traitor to Arthur thereafter.
   Arthur leaves thereafter to seek the Grail himself! Guinevere dies shortly after his departure of grief! And the story gets very different indeed from there... Lancelot is turned out of Arthur's court by the wily treachery of "Brien of the Isles," who convinces Arthur Lancelot is plotting to overthrow the High King.
   The "Perlesvaus" is the least "canonical" tale of Arthurian literature, given it's 13th Century contemporaries. It was supposed to be written as early as 1191 or as late as 1250, with most placing it between 1200 and 1215. This makes it roughly contemporary to the Vulgate.
   The Perlesvaus is quite different from the others in making Guinevere Loholt's presumed natural mother (the text does not clarify the issue, but it would be rare for a stepmother to feel such a close bond to a step-child). In the other versions of the legend such as Malory and the Vulgate, there's an unspoken possibility Guinevere is infertile; whereas Arthur proves with Lyzianor/Lionors and Margawse that he was capable of fathering sons aplenty.