Isabella Jagiellon (; ; 18 January 1519 – 15 September 1559) was the Queen consort of Hungary. She was the oldest child of Polish King Sigismund I the Old, the Grand Duke of Lithuania and his Italian wife Bona Sforza. In 1539, she married John Zápolya, Voivode of Transylvania and King of Hungary. At the time Hungary was contested between Archduke Ferdinand of Austria who wanted to add it to the Habsburg domains (see Royal Hungary), local nobles who wanted to keep Hungary independent (see Eastern Hungarian Kingdom), and Sultan Suleiman the Magnificent who saw it as a vassal state of the Ottoman Empire (see also Little War in Hungary). While Isabella's marriage lasted only a year and a half, it did produce a male heir – John Sigismund Zápolya born just two weeks before his father's death in July 1540. She spent the rest of her life embroiled in succession disputes on behalf of her son. Her husband's death sparked renewed hostilities but Sultan Suleiman established her as a regent of the eastern regions of the medieval Kingdom of Hungary on behalf of her infant son. The region developed as a semi-independent buffer state noted for its freedom of religion. Ferdinand, however, never renounced his claims to reunite Hungary and conspired with Bishop George Martinuzzi who forced Isabella to abdicate in 1551. She returned to her native Poland to live with her family. Sultan Suleiman retaliated and threatened to invade Hungary in 1555–56 forcing nobles to invite Isabella back to Transylvania. She returned in October 1556 and ruled as her son's regent until her death in September 1559. Biography Early life and marriage plans Born in Kraków on 18 January 1519, Isabella was the oldest child of King Sigismund I the Old and his Italian wife Bona Sforza. She spent most of her childhood at Wawel Castle in Kraków and the hunting castle in Niepołomice. She also lived in the Grand Duchy of Lithuania in 1527–29 and 1533–36. During the latter visit her three younger sisters were left in Kraków. This episode foreshadowed future family relationships: Bona Sforza favored her oldest daughter, arranging her marriage early, while the other three daughters were neglected and married late. Isabella received a good education, including from humanist Johannes Honter, and she could speak and write four languages: Polish, Latin, German, and Italian (her mother's native language). In March 1519, when Isabella was