Guido Reni's early biographer Count Carlo Cesare Malvasia mentions a large painting of the myth of Latona that the artist had been commissioned to paint for King Philip IV of Spain, but left incomplete at the time of his death. I argue that the canvas Malvasia describes is identical with an unfinished painting of the same subject now in a private collection in Atlanta, Georgia. This article documents the attribution and provenance of the painting, as well as its recent conservation, which has yielded important technical insights. The Spanish monarch commissioned the Latona to make amends for his Roman ambassador's hasty rejection of a previously commissioned work by Reni, the famous Abduction of Helen (Paris, Musée du Louvre), which subsequently met with extraordinary critical acclaim. I further argue that the moral argument of Reni's Latona is closely akin to that of the Helen, and, similarly selected with the advice of the papal court, was probably meant to serve as a diplomatic metaphor pertinent to ongoing political negotiations between Rome and Madrid.