 The young prince was sworn heir to the throne in 1503, the year his youngest sister, Isabella of Portugal, Empress Consort of the Holy Roman Empire between 1527 and 1538, was born.John was educated by notable scholars of the time, including the astrologer Tomás de Torres, Diogo de Ortiz, Bishop of Viseu, and Luís Teixeira Lobo, one of the first Portuguese Renaissance humanists, rector of the University of Siena (1476) and Professor of Law at Ferrara (1502).John's chronicler António de Castilho said that, "Dom João III faced problems easily, complementing his lack of culture with a practice formation that he always showed during his reign" ("Elogio d'el rei D. João de Portugal, terceiro, do nome").