This is an extraordinary example of the eventful life of many royal portraits during the Siglo de Oro, and it shows just how much those paintings, rather than immutable artworks, were objects with a representative function and could thus be altered depending on the use they were assigned at any given time. The present bust portrait depicts King Philp IV (1605-1665) in the mid 1620s, when he was just over twenty years old. It emphasizes his military responsibilities by presenting him in armor, with the crimson general´s sash across his chest. The lower half of the composition is rather anomalous as the model´s trunk appears excessively constricted by the frame, which impedes a figurative reading. This is unheard of in Velázquez, who was always extraordinarily skilled at fitting his models into the pictorial space. It is explained by the fact that, as a study of its technical characteristics has shown, this is actually a fragment of a larger canvas.

Based on that information and the model´s pose, it has sometimes been suggested that this may be a fragment of a famous equestrian portrait of Philip IV that Velázquez painted during his first years at court, which is known only from literary sources. There is no solid proof to confirm this hypothesis; moreover, the pose is similar to other portraits by Velázquez that were never equestrian. It closely resembles the portrait of the Duke of Modena (Modena, Galleria e Museo Estense), who also appears in three-quarter view, wearing armor and a red sash across his chest.

From a technical standpoint, there are striking differences between the head and the lower part. The former is rendered with more precise technique and its volumes and irregularities are meticulously shaped by the light. This approach extends to the hair, which, like the eyes, nose and mouth, is very detailed. On the other hand, both the metal and the cloth are rendered in a much freer manner, with highlights and touches of color, making them one of the first examples of what would become Velázquez´s most unmistakable technique. Such stylistic differences also appear in some of his other early works, including Democritus (Rouen, Musée des Beaux-Arts), and this has led many historians to suggest that it was painted at two different times. Thus, the first part would date from around 1625, and would encompass the face, which is constructed in a similar manner to those of the first portraits of Philip IV. X-rays have shown that this face was elaborately crafted. It has even been suggested that this may be the work on which the standing portrait of Philip IV at the Museo del Prado (P01182) is based. The sash and armor could date from a later period, judging by the stylistic differences mentioned above. This is how a work was constructed that somehow complements the early portraits of Philip IV previously discussed, as it is the first surviving portrait of that monarch by Velázquez in which the iconographic emphasis is on his military responsibilities, rather than his administrative facet.

Portús Pérez, Javier, Felipe IV (1626-1628). En Ruiz Gómez, L.: El retrato español en el Prado. Del Greco a Goya, Madrid, Museo Nacional del Prado, 2006, p.94, n. 22