Philip IV had no male heir since the death of Balthasar Charles, his son by his first wife, Elisabeth of France, eleven years before, and as Spain's strength continued to ebb the issue of succession had become a matter of fervent and anxious prayer.

A strict and devout Roman Catholic, Philip ate nothing but eggs on the first day of the Vigil of the Presentation of the Virgin, in hopes of his wife delivering a male child.

[3] Barrionuevo, a chronicler of the time, wrote of this rejoicing:[3][4] On the day of the birth, not a bench nor a table was left unbroken in the palace, nor a single pastry-cook's nor tavern that was not sacked.

There are to be masquerades, bull-fights and cane-tourneys as soon as the Queen stands up to see them, as well as plays with machinery invented by an engineer, a servant of the Nuncio, to be represented at the theatre of Retiro, and the saloon of the palace...

The municipality, following the lead of the Councils, have gone to congratulate the King... and no gentleman, great or small, has failed to do the like.To honor the birth of the new male heir, Diego Fernández de Medrano y Zeniceros, Lord of Valdeosera and Sojuela, dedicated his political treatise, Mirror of Princes: Crucible of their Virtues, Astonishment of their Failings, Soul of their Government and Government of their Soul: To the Most Serene Prince of the Spains, Don Philip Prospero, Graduated as "Optimus" by the flourishing University of Salamanca, revered as foremost in the defense of the Catholic Church, always known as August through the Generous and Valiant Imperial Blood of the House of Austria, incorporated into the Spanish August Monarchy.

In a letter to his friend Sor María de Ágreda, he wrote that "the newborn babe is doing well", but also made a reference to the bitter memory of his eldest son's demise.

[4] On 6 December 1657 Philip rode into the decorated streets of Madrid, where the preparations for the prince's baptism were almost ready: dances, masques and music greeted the King.

(These are a traditional pose and prop, though Velazquez painted the child’s sister and, years before, his half-brother Balthasar Charles with their hands in a more commanding position, placed flat and firm, not dangling.)

By contrast, nearly thirty years earlier, Velazquez painted a robust Balthasar Charles at age two or three with staff, sword, exuberant sash and plumed hat.