Constantine XI Palaiologos, the last Byzantine emperor, died defending Constantinople from the Ottomans on 29 May 1453. Andreas had been born just four months earlier, on 17 January 1453, as the oldest son of Thomas Palaiologos and Catherine Zaccaria. Following the Ottoman conquest of Constantinople, Andreas's family continued to live in the Morea as vassals of the Ottoman Sultan Mehmed II. However, constant bickering between Thomas, who tried to rally support to restore the Byzantine Empire, and his older brother Demetrios, who sided with the Ottomans, led to the Sultan invading the Morea in 1460; Thomas and his family escaped to Corfu. Thomas then left the rest of the family to go to Rome, where he was welcomed and financially supported by Pope Pius II. Thomas maintained hope that he would one day recover his lands and when preparations were being made for a crusade in 1462, which never took place, Thomas personally rode around Italy to drum up support.