The work depicts a half-length, three-quarter posed portrait of a dark-eyed woman.
We don't know who she is, or even for certain which country she's from, though her costume is typical of the beginning of the 17th century, especially in Spain.
The work is not quite finished - the face and hands are complete, but the sketching underlying the ruff still shows through, and yields some insights into the way that Rubens worked.
The painting is being sold at Sotheby's, at which another Rubens, the Massacre of the Innocents sold a few years ago for an extraordinary �49.5m - a record for an old master painting. This work, estimated at �4-6m, is unlikely to come close to that, but it has generated some genuine excitement in the art world.
Also appearing at the sale is an oval self-portrait oil-painting by Sir Anthony van Dyck. Painted at the peak of his career in 1640 it is painted confidently and shows the painter as confident, as befits the artist who was knighted and given a pension for life by Charles I.
A more recent work is Return from the Staghunt by Landseer. The landscape presents the Highland scenery in beautiful style, and captures the classic idealised view of clan life. The work, fully 63 inches long, attracted enormous acclaim when exhibited in 1837, and is listed at �800,000-1,200,000.
This exciting sale of Old Master and British paintings starts this evening at 7pm.