the daughter of Robert Corbet (Kin of Mellcene Thurman Smith, page 460)
Lady Sybilla Corbet of Alcester was born in 1077 in Alcester, Warwickshire, England. She married Herbert FitzHerbert, son of Herbert "the Chamberlain" of Winchester and Emma de Blois. She died after 1157 and was also known as Adela (or Lucia) Corbet. Sybil was definitely mother of Sybil and Rainald, possibly also of William and Rohese. Some sources suggest that there was another daughter by this relationship, Gundred, but it appears that she was thought as such because she was a sister of Reginald de Dunstanville but it appears that that was another person of that name who was not related to this family. (Wikipedia)