Charles, Prince of Viana, (May 29 1421 – September 23 1461), sometimes called Charles IV, king of Navarre, was the son of John, afterwards king of Aragon, by his marriage with Blanche, daughter and heiress of Charles, king of Navarre. Both his grandfather Charles and his mother, who ruled over Navarre from 1425 to 1441, had bequeathed this kingdom to Charles, whose right had also been recognized by the Cortes; but when Blanche died in 1441 her husband John seized the government to the exclusion of his son. The Prince of Viane was married in Olite (Navarre) on September 30 1439, taking as his wife the Flemish Princess Agnes, the daughter of Adolph I, Duke of Cleves and Mary of Burgundy sister of Philip the Good. Princess Agnes died, childless, on April 6 1448, eight years after her marriage to Charles.

The ill-feeling between father and son was increased when in 1447 John took for his second wife Joanna (Juana) Enriquez, a Castilian noblewoman (of a bastard cadet line from Castilian kings), who soon bore him a son, afterwards Ferdinand V, king of Spain, and who regarded her stepson as an interloper. When Joanna began to interfere in the internal affairs of Navarre, civil war broke out, and in 1452 Charles, although aided by John II, king of Castile, was defeated and taken prisoner. Released upon promising not to take the kingly title until after his father's death, the prince, again unsuccessful in an appeal to arms, took refuge in Naples with Alphonso V, king of Aragon, Naples and Sicily. In 1458 Alphonso died and John became king of Aragon, while Charles was offered the crowns of Naples and Sicily. He declined these proposals, and having been reconciled with his father returned to Navarre in 1459. Aspiring to marry a Castilian princess, he was then thrown into prison by his father, and the Catalans rose in his favor. This insurrection soon became general and John was obliged to yield. He released his son, and recognized him as perpetual governor of Catalonia, and heir to the kingdom.

Soon afterwards, however, on 23 September 1461, the prince died at Barcelona, not without a suspicion that he had been poisoned by his stepmother. He was promised to marry Catherine of Portugal (daughter of Portuguese King Edward I) when he died.

Charles was a cultured and amiable prince, fond of music and literature. He translated Aristotle's Ethics into Spanish, a work first published at Saragossa in 1509, and wrote a chronicle of the kings of Navarre, Cronica de los reyes de Navarra.

By Brianda Vaca, he had an illegitimate son, Philip, who became Archbishop of Palermo. He also had several other illegitimate children.

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