Carlos II was the last of the Habsburg dynasty to rule Spain. Known as 'the Bewitched' he suffered from physical and intellectual disabilities cause by generations of inbreeding and was regarded as a weak and ineffectual ruler. At his death he left the Spanish throne to his grand-nephew, Philip of Anjou, causing fears over a Franco-Spanish alliance which ultimately led to the War of Spanish Succession.

Juan Bautista Martínez del Mazo was the son-in-law of Diego Velázquez. He probably entered the studio of Velazquez in 1630 and married his master's daughter in 1633. From that date he was closely associated with his father-in-law and assisted Velázquez in the production of court portraits. Velázquez, who then held the position, arranged for Philip IV to appoint Mazo Ujier de Cámara in 1634, enabling Mazo to enter court circles and from 1643 he served as professor of painting and painter to the Infante Balthasar Carlos until the latter's death in 1646. After the death of Velazquez in 1660, Mazo succeeded his father-in-law as Pintor de Cámara (court painter) to Philip IV of Spain and on the death of the old king in 1665, fulfilled the role under Carlos II until his own death in 1667.

Although his life is well documented, Mazo style so closely imitated that of his father-in-law that very few surviving works can be securely attributed to him. A full-length portrait of Infante Balthasar Carlos in the Royal Collection and another version in the Mauritshuis are firmly attributed to Mazo, as is Child Wearing Ecclesiastical Robes (Toledo Museum of Art), Portrait of the Painter's Family (Kunsthistorisches, Vienna) and a portrait of Mariana of Austria in the National Gallery, London.

This portrait shows the young Carlos II at full-length. The inscription at the bottom of the painting giving the king's age as four and the date as 1665 is on a separate piece of canvas and was almost certainly added later, although the information would appear to be accurate. The infant king is shown dressed in a black suit and cape, and a large plumed hat, possibly in mourning for his late father Philip IV, who died in September 1665. He holds a sceptre in his left hand, close to a table on which rests a red cushion supporting the crown. To the king's right is the symbolic lion of Spain, recumbent beside a red-covered chair. Carlos II wears the Order of the Golden Fleece and the hilt of a silver ornamented sword is visible by his left cuff, enhancing the formality and solemnity of the portrait. The inclusion of a table had been customary in indoor portraits of Spanish kings since Titian's portrait of the future Philip II, painted in Bologna in 1551 (Museo del Prado, Madrid) and the device had been used Velazquez in his portraits of both Philip IV (RCIN 402914) and Balthsar Carlos. This composition was plausibly painted by Mazo to mark the young king's accession to the throne; however, no autograph versions of the portrait are known and the quality of the draughtsmanship and brushwork, particularly in the rendering of the lion suggest the participation of a studio assistant in the completion of this work.Several similar versions of the composition are known; an anonymous work in the Royal Monastery of San Lorenzo de El Escorial, in which the infant king holds an orb a well as a sceptre but which is otherwise close to the Royal Collection painting and another anonymous version in the Museo del Prado (P002534). In the latter, the recumbent lion is missing and a dog has been added.