The youth of Prince Alfonso who would become King Alfonso XII of Spain after Queen Isabel II abdication, centered in his love for his cousin María de las Mercedes. Daughter of one of his mother's political opponents, their marriage against the Queen's will won for them popular approval and helped achieving political stability in a turmoiled country. Her early and tragic death would inspire the song of the film's title. The film was so successful that a second part ("¿Dónde vas triste de ti?") would follow.