The portrait is an early example of the artist's Italian period
A previously unrecorded portrait of a mystery woman by Sir Peter Paul Rubens could fetch £6m when it goes on sale in London next week.
The painting, which remains partly unfinished, shows a female subject who is thought to be Spanish.
Experts believe the work was created in the early 17th century when the Flemish artist travelled to the Mediterranean.
The portrait will go under the hammer at Sotheby's evening sale of Old Master and British paintings on 9 December.
The work is thought to have stayed in Venice and elsewhere in Italy until the early 19th century.
It was then acquired for the private collection of the Hammer family and was at their home in Wales out of public view.
Rubens is thought to have been commissioned by his aristocratic patron to paint portraits of Spanish ladies for his gallery, but it is unclear whether this is one of them.
The reason why he did not complete the portrait is also not known.
In 2002, Rubens' Massacre of the Innocents was sold for £49.5m at auction, setting a record for a work by an Old Master.