A charter of Bishop Franco of Paris dated May 26, 1028, tells us that during the war between the counts Bouchard of Vendôme and Eudes of Blois, the count of Château-Landon (Gâtinais) was a Geoffroy, and that his son and heir was count Aubry, whose half-brothers (by the same mother) and heirs Geoffroy and Liétaud were sons of Hugues du Perche. This half brother Geoffroy was almost certainly the Geoffroy count of Gâtinais, the father of Fulk IV an Geoffroy III le barbu.

["In nomine regis eterni. Ego Franco, annuente Dei clementia, Parisiorum humilis episcopus. Notum fieri volumus tam presenti aetati quam future posteritati, quia domus Rainaldus episcopus, noster predecessor, dedit quasdam villas, inconsulte et absque consilio regalis potestatis, de mensa Episcopi, videlicet Buxas et Scabiosas, sitas in comitatu Gastinensi, Gofrido, comiti Landonensis castri; quod et factum est pro nulla utilitate ecclesie, sed propter guerram et discordiam que tunc temporis erat inter patrem suum nomine Burchardum, et comitem Odonem, quod ita longo tempore permancit. Postea vero, auxiliante Domino nostro atque genetrice ejus Maria, necnon patrocinante juvamine domini nostri piisimi regis Reberti atque Constantie, ejus conjugis, nobilissime regine, et per nostram apud eos humilem deprecationem, talis facta est conventio inter nos et Albericum, illius supradicti Gosfredi filium et heredem, et insuper faventibus fratribus ipsius Alberici, filiis Hugonis Pertice, scilicet Gosfredo et Letoldo, quia unam ex ipsis potestatibus, nomine Scabiosas, cum ecclesia que est in illa villa, reddiderunt; alteram vero ecclesiam, que est in villa que dicitur Buxas, similiter reddiderunt, ea videlicet ratione ut, quamdiu Adraldus clericus advixerit, eamdem ecclesiam teneat nobisque censum de ea reddat, et post ejus ad hac vita discessum, ad jus Sancte Marie et nostrum redeat. Cetera autem ad easdem villas pertinentia, ipsi Alberico et duobus heredibus ejus per manus firmitatem concedimus; eo videlicet tenore ut omni anno, in festivitate Sancte Marie, que est VI idus septembris, in censum x solidos denariorum ad mensam nostram persolvant. Quod si inde negligentes apparuerint, legaliter emendent et minime perdant. Ut autem hec manus firmitas vigorem per omnia teneat, auctoritate domini nostri regis et regine atque prolis eorum, manu propria eam firmavimus, fidelibusque nostris clericis et laicis corrobandam tradidimus. Actum apud monasterium Kalas, VII kal. junii, regnante serenissimo rege Rotberto anno XXXo, Henrico autem ejus filio IIo, S. Rotberti regis, S. Henrici regis, S. Constantie regine, S. Rotberti ejus filii, S. Franconis episcopi, S. Gosfredi decani, S. Obrici archidiaconi, S. Lisiermi archidiaconi, S. Alberti archidiaconi ..., S. Waleranni comitis, S. Dragonis comitis ... Harduinus scripsit atque recensuit vice Lantberti cancellarii."]

The Saint-Aubin genealogies, evidently composed during the reign of Fulk IV, not only give the name of the father of Fulk IV and his brother Geoffroy III le Barbu, but provide the maternal ancestry of their father as Beatirx, daughter of Albericus, son of Letaldus ["Letaldus comes Vesconsiosis (et Umbertus comes Matisconiensis fratres fuerunt ...); ex Letaldo Albericus natus est; ex Alberico Beatrix; ex Beatrice Gosfridus comes de Castello Landonensi. Ex Gaufrido Gaufridus et Fulco presens."].

Although Bishop Franco of Paris does not explicitly identify the woman who married both Geoffroy of Gâtinais and Hugues du Perche, it is not difficult to see that she was the same person as the Béatrix mentioned in the Saint-Aubin genealogies. Béatrix's son Geoffroy could not be the count who died before 1028 because had to be living in the early 1040's to be the father of Fulk IV. Béatrix's husband could not have been count Aubry, since he had no children in 1028 (his half-brothers were his heirs) and any child of his born after 1028 would be too young to be the father of Fulk IV and Geoffroy III. Also, Béatrix named her sons Aubry and Liétaud after her father and grandfather.

Weis makes the father Geoffrey III, Count of Gatinais.