[2] His father essentially transferred the reign of Flanders to him in November 1299, during his war with Philip IV of France.

Robert of Béthune gained military fame in Italy, when he fought at the side of his father-in-law, Charles I of Sicily (1265–1268) against the last Hohenstaufens, Manfred and Conradin.

Guy of Dampierre broke all feudal bonds with the French king (on 20 January 1297) mainly under his influence.

When the resistance seemed hopeless Robert allowed himself to be taken prisoner, together with his father and his brother William of Crèvecoeur, and taken to the French King (May 1300).

Contrary to popular belief, and the romantic portrayal by Hendrik Conscience in his novel about these events (The Lion of Flanders), he did not take part in the Battle of the Golden Spurs.

When his grandson Louis I of Nevers pressured him as well, Robert gave up the battle and went to Paris in 1320 to restore feudal bonds with the French King.