Prince Baltasar Carlos was the only son of Philip IV and his first wife, Elisabeth of France (Isabel de Borbón). The present painting is based on a full-length portrait of around 1640 or slightly earlier in the Kunsthistorisches Museum, Vienna (fig. 1). Traditionally regarded as a collaborative effort between Velázquez and his workshop, the overall design and head of the Vienna portrait are thought to be by the master and the remainder by one or more workshop assistants (see J. López-Rey, Velázquez: Catalogue Raisonne; Werkverzeichnis, Cologne, 1996, I, p. 188, II, p. 222, no. 90). It has been suggested that the workshop collaboration in the Vienna portrait is due to the 1643 appointment of Velázquez’s son-in-law, Juan Bautista Martínez del Mazo (c. 1613-1667), as court painter to the prince, a position he held until the boy’s premature death from smallpox in 1646 (see J. Brown, Velázquez: Painter and Courtier, New Haven and London, 1986, p. 169). An attribution of the present painting to Mazo may be considered.
Generally regarded as an autograph work by Velázquez throughout the 19th century, the present painting has a distinguished history. It was one of four portraits of the Prince exhibited at the fabled Art Treasures Exhibition held in Manchester in 1857, the other three having been lent by Richard Seymour Conway, 4th Marquis of Hertford (1800-1870), and residing today in the Wallace Collection, London. Later, it was part of the seminal collection of fifty European paintings—including Johannes Vermeer’s magnificent Young Woman with a Water Pitcher—that Henry Gurdon Marquand, whom one contemporary described as "the greatest collector in America," donated to the Metropolitan Museum of Art in 1889.