General Notes

Rollo, or Fulbert, chamberlain to Robert, Duke of Normandy, had the gift of the castle and honor of Croy, in Picardy, from whence his posterity assumed their surname, which was afterwards written de Grey. They had a daughter Hervela or Herlotta, who was the mother of William, the Conqueror, and a son, Reynold.
Sources: Burke's Dormant and Extinct Peerage, p. 248.
Edmondson's Baronagium Genealogicum, Vol. 1, p. 77; Vol. 4, p. 340.
Glover's History and Gazeteer of Derbyshire, Vol. 2, pp. 308/9.
Lipscomb's History of Buckinghamshire, Vol. 1, pp. 160, 466.
Banks Dormant and Extinct Baronage, Vol. 2, p. 224.
Lewis' Manuscripts, pp. 154, 267.
Cokayne's Complete Peerage of Great Britain, Vol. 4, pp. 308-311, 761,
Appendix No. 1.