According to Ulrich's Lanzelet, a paramour of Lancelot. She was the daughter of the famous huntsman Patricius von den Bigen (of the Mound), and she was raised by her uncle, Linier, in the castle Limors.
Lancelot came to Limors during his early adventures, and ran afoul of the ill-tempered Linier even as Ade cast eyes his way. Lancelot ended up killing Linier in combat, and he and Ade became paramours. Ade gave him her brother Tybalt as a squire.
During an outing, Lancelot succumbed to the enchantment of the Schatel le Mort, which turned brave knights into cowards. Ade, seeing Lancelot acting cowardly, and not knowing of the enchantment, abandoned him in disgust and never saw him again.
Ade is not found in any other romance. It seems more than a coincidence that Hugh de Morville (who provided Ulrich with his source) had a mother and daughter named Ada.