The title of "Duke of Brabant" was granted for the first time in the Belgian dynasty to Prince Leopold, eldest son of King Leopold I. By granting this tile, it was intended to associate the Princes, from their very youngest years, with the feelings and memories of their homeland
After King Albert I was sworn in, it was decided that the title of "Duke of Brabant" would henceforth be given to the King's eldest son, or if he had no son, by the eldest grandson of the Sovereign. This title would precede that of "Prince of Belgium".
Prince Leopold bore that title until 1934, when he succeeded his father to become King Leopold III. It was Prince Baudouin, his eldest son, who then bore the title until his accession to the throne in 1951.
This title does not allude to the former province of Brabant, but rather to the Duchy of Brabant, the main region of the Habsburg Netherlands.