Ferdinand the Holy Prince (; ; 29 September 1402 – 5 June 1443), sometimes called the "Saint Prince" or the "Constant Prince", was an infante of the Kingdom of Portugal. He was the youngest of the "Illustrious Generation" of 15th-century Portuguese princes of the House of Aviz, and served as lay administrator of the Knightly Order of Aviz. In 1437, Ferdinand participated in the disastrous Siege of Tangier led by his older brother Henry the Navigator. In the aftermath, Ferdinand was handed over to the Marinid rulers of Morocco as a hostage for the surrender of Ceuta in accordance with the terms of a treaty negotiated between the rulers of Portugal and Morocco by Henry. At first, Ferdinand was held in relative comfort as a noble hostage in Asilah, but when it became apparent that the Portuguese authorities had no intention of giving up Ceuta, Ferdinand's status was downgraded; he was transferred to a prison in Fez, where he was subjected to much harsher incarceration conditions by his jailers. Negotiations for his release continued intermittently for years, but they came to naught, and Ferdinand eventually died in captivity in Fez on 5 June 1443. A popular cult quickly developed in Portugal around the figure of "the Holy Prince" (O Infante Santo), strongly encouraged by the House of Aviz. Ferdinand remains a "popular saint" by Portuguese tradition, neither beatified nor canonized by the Catholic Church. Early life Ferdinand was the sixth and youngest son of King John I of Portugal and his wife Philippa of Lancaster. Ferdinand and his brothers Edward of Portugal, Peter of Coimbra, Henry the Navigator and John of Reguengos, plus sister Isabella of Burgundy and half-brother Afonso of Barcelos, constitute what Portuguese historians have traditionally labelled the 'illustrious generation' (Ínclita Geração). Ferdinand was born in Santarém on 29 September 1402, the feast day of St. Michael, a saint to whom he would remain affectionately attached. He had a complicated birth and would remain a sickly child throughout much of his youth. Relatively sheltered because of his illnesses, Ferdinand had a quiet and very pious upbringing, a favorite of his English mother, from whom he acquired a preference for the Sarum Rite of Salisbury in the religious liturgy of masses he attended. Master of Aviz Ferdinand was too young to participate in the 1415 Conquest of Ceuta led by his father, John I, in which his older brothers