Couronne de saint Étienne
Soon after John Zápolya died, his treasurer, George Martinuzzi, hurried to Buda to secure John Sigismund's inheritance. On Martinuzzi's proposal, the Diet of Hungary elected John Sigismund king on 13September 1540, but he was not crowned with the Holy Crown of Hungary. The Diet proclaimed Queen Isabella and George Martinuzzi, along with two powerful lords, Péter Petrovics and Bálint Török, the guardians of the infant monarch.