Sigismund made Vlad a first-class member of the Order of the Dragon (a chivalric order established by Sigismund) in Nuremberg on 8 February 1431. Other first-class members included Alfonso V of Aragon and Vytautas, Grand Duke of Lithuania. The dragon-shaped badge of the order gave rise to his Romanian sobriquet, "Dracul" ("the Dragon"), for which his sons became known as "Dracula" ("son of Dracul"). Vlad swore fealty to Sigismund who declared him the lawful prince of Wallachia. Vlad had to promise that he would protect the Roman Catholic Church. However, Sigismund did not assist him to seize Wallachia. In the summer, Vlad's half-brother, Alexander I Aldea, invaded Wallachia with Moldavian support and dethroned Dan II.