Poor Mariana! Marrying at age fifteen (15) the 45 years old father of your initially intended fiancé (who died 2 years before). Giving duly birth at age seventeen. Subsequently being ill for many months. And when you have finally recovered you have to pose for the court painter while you’re incarcerated in a huge stiff unwieldy dress.
You look as if you’re about to burst into tears.
But don’t think art history will take pity on you! Oh no, more than 300 years later a meticulous art historian will dismiss you as surly, obstinate, bad-tempered. He will deplore your extremely ungainly appearance but will nevertheless praise the beauty of the picture, viewed as a painting.
From Joseph-Emile Muller : Velázquez (Thames & Hudson 1976)
"[Princess Mariana of Austria] had once been the intended wife of Baltasar Carlos and was now to be married instead to Philip IV, her uncle and the father of the man to whom she had been betrothed. At the end of 1648 the Princess was just fourteen years old and the King forty-four. [They married in October 1649]
Velázquez did not paint her at once because she was about to give birth, and even after Princess Margarita was born, in 1651, she was unwell for several months. But in 1652 she sat for a huge portrait. Here her face is not the most important feature – which is no particular loss as it is not especially attractive. At scarcely eighteen years of age this young woman looks proud, surly, obstinate, bad-tempered and utterly lacking in spontaneity. […] The dress [flattens] the bosom into a tight bodice and billows out around the body, hiding it completely. […] It is hard to imagine a more extreme negation of femininity or a more ungainly appearance. Nevertheless, if one studies the picture for a while, one is struck less by the ugliness of the attire than by the beauty of the picture, viewed as a painting."