Fernando, the Saint Prince, of Portugal (d. 1443)
Ferdinand the Holy Prince (Portuguese pronunciation: [fɨɾˈnɐ̃du]; Portuguese: Fernando o Infante Santo; 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 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, and 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.