John Sigismund Zápolya or Szapolyai (; 7 July 1540 – 14 March 1571) was King of Hungary as John II from 1540 to 1551 and from 1556 to 1570, and the first Prince of Transylvania, from 1570 to his death. He was the only son of John I, King of Hungary, and Isabella of Poland. JohnI ruled parts of the Kingdom of Hungary with the support of the Ottoman Sultan Suleiman; the remaining areas were ruled by Ferdinand I of Habsburg, who also ruled Austria and Bohemia. The two kings concluded a peace treaty in 1538 acknowledging Ferdinand's right to reunite Hungary after JohnI's death, though shortly after John Sigismund's birth, and on his deathbed, JohnI bequeathed his realm to his son. The late king's staunchest supporters elected the infant John Sigismund king, but he was not crowned with the Holy Crown of Hungary. Suleiman invaded Hungary under the pretext of protecting John Sigismund from Ferdinand. Buda, the capital of Hungary, fell to the Ottomans without opposition in 1541, but Suleiman allowed the dowager queen, Isabella, to retain the territory east of the river Tisza on John Sigismund's behalf. Isabella and John Sigismund moved to Lippa (now Lipova in Romania). Before long, they took up residence in Gyulafehérvár in Transylvania (Alba Iulia in Romania). John Sigismund's realm was administered by his father's treasurer, George Martinuzzi, who sought to reunite Hungary under the rule of Ferdinand. Martinuzzi forced Isabella to renounce her son's realm in exchange for two Silesian duchies and 140,000 florins in 1551. John Sigismund and his mother settled in Poland, but she continued to negotiate for John Sigismund's restoration with Ferdinand's enemies. Ferdinand was unable to protect eastern Hungary against the Ottomans. At Suleiman's urging, the Transylvanian Diet in 1556 persuaded John Sigismund and his mother to return to Transylvania, where she ruled her son's realm until her death in 1559. A wealthy lord, Melchior Balassa, rebelled against John Sigismund in late 1561, and Ferdinand gained control of most counties outside Transylvania. The Székely people, whose liberties had been restricted in the 1550s, also rose up against John Sigismund, but he crushed the rebellion. During the ensuing war against the Habsburgs, the Ottomans supported John Sigismund, and he paid homage to Suleiman in Zemun in 1566. The 1568 Treaty of Adrianople concluded the war, confirming John Sigismund in the eastern territories of the medieval Kingdom of Hungary (Transylvania