John, Prince of Asturias and Girona (Spanish: Juan; 30 June 1478 – 4 October 1497) was the only son of King Ferdinand II of Aragon and Queen Isabella I of Castile, and heir apparent to both their thrones for nearly his entire life.

[1] At the time, his parents were involved in the War of Castilian Succession against Isabella's niece Juana la Beltraneja, wife of King Afonso V of Portugal.

[13] Isabella and Ferdinand attempted to ensure the sickly prince's well-being through prayer, charity, and careful oversight of his health.

[12] In 1492, Columbus named the newly discovered island of Cuba as Isla Juana in deference to Prince John, at that time the heir apparent.

[19] John, Prince of Asturias, as the sole male heir of the Catholic Monarchs, Ferdinand II of Aragon and Isabella I of Castile, received a rigorous education tailored to prepare him for his future role as a ruler.

His first preceptor was the Dominican friar Diego de Deza, a distinguished theologian who later became the Bishop of Salamanca and Inquisitor General of Spain.

[22] Under Deza’s guidance, John was instructed in Latin, theology, and moral sciences, with a strong emphasis on Christian doctrine.

[23] In 1492, Queen Isabella expanded John’s education by appointing the Italian humanist Peter Martyr d'Anghiera as his personal tutor.

This reflected the Renaissance ideals spreading across Europe, marking a shift from purely religious instruction to a more rounded educational approach.

His musical abilities were not merely for personal enjoyment; they also played a role in his public image, showcasing his refinement and cultural sophistication—a valued trait in Renaissance courts across Europe.

[12] His frailty likely influenced the pace and intensity of his studies, as his tutors had to balance rigorous training with the reality of his physical limitations.

This delicate balance was a constant concern for his parents, who were deeply invested in ensuring that their only son was well-prepared to unify the crowns of Aragón and Castile, despite the ever-present threat of his declining health.

[28] Seeking Emperor Maximilian I's participation, Ferdinand engaged in negotiations for dynastic marriages between the Habsburg and Spanish royal families, aiming to seal the prospective alliance between the Holy Roman Empire and Spain.

[37] In September 1497, John's fragile health prevented him from joining his parents and sister, Infanta Isabella, as they journeyed to the Portuguese border for her wedding to Manuel I.