The False Guenevere
Gonnere, Gonnore, Guineure, Guenievre, Gueonivre, Gyennevre
King Leodegrance was a busy man. On the same night he engendered Guenevere on his wife, he engendered a second daughter on the wife of Cleodalis, his seneschal. The two children were born on the same day, looked exactly alike (despite having different mothers), and, just to keep things simple, Leodegrance gave them both the same name.
Sommer distinguishes the bastard daughter as "the false Guenevere", but this seems to me unfair - it was not her fault she was born with Guenevere's looks, and she had just as much right as the true-born daughter to the name she was given. Therefore, I have used an alternate spelling for the name Guenevere - the spelling Sommer gives both Gueneveres in Vulgate II - for this second one.
Genievre was raised as the supposed daughter of Cleodalis, which must have been either a good trick or a courteous pretense, considering her looks and name. Rich relatives of Cleodalis, hating Leodegrance, tried to substitute Genievre for Guenevere on Arthur's wedding night, but the attempt to kidnap Guenevere was foiled by Ulfius and Brastias. At Leodegrance's order, Cleodalis took Genievre away from Carohaise; he also disowned her. On the same night as the attempted abduction, Bertholai, one of Leodegrance's knights, murdered another knight out of hatred, and was disinherited and banished for the deed. Some time afterward, Bertholai came to the place where Genievre was living.
Championed by Bertholai, this Guinevere claimed that she was the true Guinevere and enticed Arthur into giving up her half-sister. The true Guinevere then took refuge in Sorlois. In the end she and her champion admitted their deception and, after two and a half years, Arthur and the real Guinevere were reunited.