|Peter Paul Rubens, ca. 1625|
Formerly it was assumed that the sitter was a chambermaid of Infanta Isabella, the Governess of Netherlands. However, it is believed - because of the similarity to a drawing of Isabella Brandt (Rubens' first wife) in the British Museum, London - to be a posthumous portrait of Rubens' daughter Clara Serena (1611-1623).
Source: The Web Gallery of Art