In 1813 he was appointed and sent as French Ambassador at Vienna, where he was engaged in an unequal diplomatic duel with Metternich during the fateful months that witnessed the defection of Austria from the cause of Napoleon to that of the Allies, to confirm the alliance between France and Austria, objective he was not able to fulfill; the Empire had its days cut short. In that same year he was appointed Governor of the stronghold of Torgau (Saxony), one of the main strategic points for the defense of the Empire. On 17 November 1813, after reviewing the troops on horse, he died of typhus. His aide-de-camp, Captain comte de Rohan-Chabot, brought his heart back to France, and afterwards the name of the comte de Narbonne-Lara was inscribed on the east side of the Arc de Triomphe.