House of Farnese
He competed for the Grand Mastery of the Sacred Military Constantinian Order of Saint George, whose obscure magisterial dynasty was going extinct in the late 17th century, and whose grand mastership had been transferred to Francesco Farnese, Duke of Parma in 1696. In the annals of that chivalric institution and of the Vatican, Gustav is referred as a "Duke of Bavaria". Gustav failed in his aspirations, and the grand-mastership was confirmed in 1701 by the pope to be hereditary in the House of Farnese and its successors (the Dukes of Castro). The Farnese duke was later succeeded in the position by his nearest male kinsman, the future king Charles III of Spain.