It is thought Lady Stanhope and van Dyck were romantically linked
A portrait of a London society lady by her lover, artist Sir Anthony van Dyck, is to go on display for the first time in over a century.
The picture of Katherine, Lady Stanhope - later Countess of Chesterfield - will form part of Tate Britain's forthcoming exhibition, van Dyck and Britain.
It was thought the portrait was missing until it was put up for auction in New York in 2006.
The exhibition, featuring 130 works by Van Dyck, opens on 18 February 2009.
A letter from Lord Conway to Lord Wentworth in 1636 described van Dyck's "Gallantrye for ye love of that Lady".
The letter also described a dispute between the pair about the price of the painting.
It is not clear whether Lady Stanhope commissioned the portrait or if it was a gift.
The painting will be displayed along with over 130 works by van Dyck and other British artists whose work he influenced, from the 17th to the 20th centuries.
The exhibition will include paintings from the Royal Collection, the National Trust and many private collections.