The following information was supplied in a post-em by Curt Hofemann, curt_hofemann@@yahoo.com:
aka: Guillaume de 'Simplex' de Blois, Seigneur de Sully simplex = simple (minded). Burke's Peerage 1919 p24 says he was "an imbecile".
Count of Chartres, j.u. Sire de Sully [Ref: Paget p10] Lord of Salejo, Sire De Sully [Ref: Moriarty, Turton] (I think "Sire" should be "Seigneur" & unable to locate "Salejo" which looks Spanish, not French. Also, in French is there a differentiation of Lord vs Sire?... Curt)