"Roberti filius eius [Robertus Flandrensium comes]" is named in the Cartulaire de Saint-Bertin. The Genealogica Comitum Flandriæ Bertiniana names (in order) "Philippum et Robertum" as sons of "Robertus [et] vidua Gertrude".
He ruled with his father as joint count of Flanders from 1086. He succeeded his father in 1093 as ROBERT II Count of Flanders. He joined the First Crusade in 1096, and was joint-leader of a contingent with Robert Duke of Normandy and Etienne Comte de Blois. As the crusaders approached Antioch in Oct 1097, a contingent under Count Robert captured Artah to the south-west. After the capture of Jerusalem, he left Palestine for Europe in Sep 1099. He helped Henry I King of England conquer Normandy from his brother Robert in 1106, in accordance with the alliance agreed in the Treaty of Dover in 1103 which was renewed in 1110.
Orderic Vitalis records that Count Robert was among the forces of Louis VI King of France which fought Thibaut IV Comte de Blois near Meaux, that he was trampled as the king fled with his men, and died a few days later. According to William of Malmesbury, he was mortally wounded in a tournament.
The necrology of the abbey of Saint-Denis records the death "III Non Oct" of "Rotbertus Flandrensium comes", which is consistent with the date of death of Count Robert II shown in Europäische Stammtafeln. However, it seems more likely that this entry relates to Count Robert I... as the same necrology also records the death "XV Kal Aug" of "Gertrudis comitissa" who may be identified with the wife of the older count Robert. 1
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