The Chronicle of Foulque le Réchin, allegedly written by Fulk IV, states that Ermengarde was a daughter of Fulk III "Nerra", sister of Geoffroy II "Martel", wife of count Geoffroy of Château-Landon, and mother of Fulk IV and Geoffroy III le Barbu. Some twelfth century sources which incorrectly list Fulk IV's father, list her mother as Adela. In a genealogy of the Counts of Anjou her father is listed as Fulco and her mother as Hildegardis ["Fulco (pater) Gosfridus et Ermengardis (mater) Gosfridus (et) Fulco (et) Hildegardis, de altero patre, filia Roberti ducis fratris Henrici regis"].
It is confirmed that his father married Hildegarde through various charters. His parents, ["Fulco Andegavorum comes atque Hildegardis conjunx mea"] founded the monastery of La Charité Sainte-Marie d´Anjou by undated charter signed by ["…Goffridi Fulconis filii…"] and [Fulco Andecavorum comes et uxor mea Hildegardis filius quoque noster Goffridus"] donated the bridge of Mayenne to the monastery of La Charité Sainte-Marie d´Anjou by undated charter.