In Chrétien's love triangle of Arthur-Guinevere-Lancelot, Guinevere consummated her love affair with Lancelot when Arthur and his knights are trying to rescue Guinevere from the land of Gorre. It has been suggested that Chrétien invented their affair to supply Guinevere with a courtly extramarital lover (as requested by his patroness, princess Marie); Mordred could not be used as his reputation was beyond saving, and Yder had been forgotten entirely.[36] This version has become popular. Today it is most familiar from its expansion in the prose cycles, where Lancelot comes to her rescue on more than one occasion.

The Knight of the Cart is believed to have been a story assigned to him by Marie de Champagne, and completed not by Chrétien himself, but by the clerk known as Godefroi de Leigni.[3] A 12th-century French writer usually functioned as a part of a team, or a workshop attached to the court. It is believed that in the production of The Knight of the Cart, Chrétien was provided with source material (or matiere), as well as a san, or a derivation of the material. The matiere in this case would refer to the story of Lancelot, and the san would be his affair with Guinevere. Marie de Champagne was well known for her interest in affairs of courtly love, and is believed to have suggested the inclusion of this theme into the story. For this reason, it is said that Chrétien could not finish the story himself because he did not support the adulterous themes.[4]

So apparently medieval literature had a concept of fan fiction and Lancelot as we know him was the product of Princess Marie commissioning a story where Guinevere fucks a hot guy