In The School For Good and Evil
Guinevere was mother to Tedros. Only mentioned briefly in the first book, Guinevere was implied to be the main reason for Tedros' fear of romantic dishonesty. Unlike in her legend, she did not return to King Arthur.
Guinevere was found to be hiding in Avalon's safe house in the Last Ever After, along with Lancelot. The only two who knew of their whereabouts were Merlin and the Lady of the Lake, who originally hid them. She was ashamed of how she abandoned Tedros, but she reconciled with him after Agatha convinced Tedros to talk to her. She also revealed that she kept her royal crown, and gave it to Agatha the morning after Sophie returned to the School Master. Guinevere explained that it was her duty as Camelot's queen to give the crown to the next queen, and she managed to encourage Agatha past her self-doubt by helping the girl focus on what being queen means. She stayed in Avalon during the battle of the Stymph Forest, but later accompanied Tedros and Agatha to Camelot at the end of the book along with Lancelot and Merlin.
Guinevere, Arthur, Lancelot : Love Triangle
Guinevere met Arthur in The School For Good. Arthur fell over heels to Guinevere, even, obsessed with her. He would scheme Guinevere for ensuring Guinevere that Arthur was her true love. Guinevere had an interest in Arthur's best friend, Lancelot, who also happened to be bookish and an animal-lover. Arthur noticed their relation but he made sure Lancelot knew that Arthur had an interest in Guinevere. Arthur persuaded Guinevere he was the right choice for husband. Beside, How could Guinevere marry a knight to a king, while Guinevere could have the king himself?
They soon married and had a baby named Tedros of Camelot. Even though they were "happy", Arthur still had a suspicion against Guinevere and Lancelot. He controlled Guinevere and he came to Merlin for a spell that could verify Guinevere's faithfulness. But Merlin told him to let Guinevere go. Arthur was mad and he stole the sex-switching potion. Guinevere then fled with Lancelot, leaving Tedros and Arthur alone. Arthur commanded a warrant on Guinevere's head and Merlin also went away.
In Arthurian Legend
Guinevere was the wife of King Arthur, the legendary ruler of Britain. She was a beautiful and noble queen, but her life took a tragic turn when she fell in love with Lancelot, one of Arthur's bravest and most loyal knights. The relationship between the queen and Lancelot eventually destroyed the special fellowship of the Knights of the Round Table.
Guinevere was the daughter of King Leodegrance of Scotland. Arthur admired the king's lovely daughter and married her in spite of a warning from his adviser Merlin that Guinevere would be unfaithful to him. As a wedding gift, Leodegrance gave Arthur a round table that would play a central role in his court.
After the marriage, Guinevere became acquainted with Lancelot, who performed various deeds to honor and rescue her. At first, Arthur took no notice of the growing attachment between the queen and Lancelot. Later, however, the king was forced to accuse his wife of adultery and to fight her lover. Several violent battles between Arthur and Lancelot followed, with groups of knights joining in on each side. Eventually, Guinevere returned to Arthur.