Isabeau, also known as Isabeau de Bavière (イザボー・ド・バヴィエール Izabō do Bavuiēru), is the main antagonist in Puella Magi Tart Magica: The Legend of "Jeanne d'Arc". She is the Queen of France.
- Eye colour: Yellow
- Hair colour: Blonde
- Soul gem: Oval gem at the center of her necklace (largest oval)
- Witch form: Crépuscule de La Reine
- Wish: For everything you (Kyubey) possess.
- Japanese pronoun:
- Known relatives: Charles VI of France (husband), Corbeau, Lapin and Minou (adoptive daughters)
Because of her wish, Isabeau gained the same abilities and knowledge as Kyubey, making her partly an Incubator, magical girl, and ultimately a witch. She could create magical girls and grant their wishes and her body also couldn't be permanently destroyed. Despite that, she still possessed a soul gem and became a witch; as she did have Kyubey's powers, she could never be exactly like Kyubey as the transformation from magical girl to witch only happens to life-forms other than him. When she became a witch, her wards encased all of France, allowing witches to be seen by humans. Any girl who contracted with Isabeau after her transformation lost their wills and souls, and Kyubey notes that this prevented his race from collecting the energy made by those magical girls when they became witches. When Isabeau died, the magic of her contracts caused Minou (her remaining daughter) to become a normal girl again as Isabeau was an imperfect creator.
Due to the wishes of Minou and Lapin, she became a witch in a human shell and couldn't be defeated by any ordinary magical girl with the exception of Tart.
- Out of all the witches that appear in Tart Magica, Isabeau's witch is the only one that is named.
- Her witch name is French and translates to, "Twilight of the Queen".