References for Richard III. 6th Earl, 4th Earl de Clare * of Clare * of Hertford and Gloucester
E. Brandenburg: Die Nachkommen Karls des Grossen. Leipzig 1936, Frankfurt 1964
F.M.Powicke, E.B.Fryde: Handbook of British Chronology. London, 1961
D.Schwennicke: Europäische Stammtafeln, Vol. III/1, Tafel 156. Marburg, 1984