The portrait of one of the artist’s children, Isobel Boyt, has not been seen in public for over two decades. It is set to go on sale at an auction next week.

Ib Reading was the result of more than 70 sittings by Boyt in the artist’s studio in Holland Park, west London, in 1997. Known to her family as Ib, Boyt is painted while reading Marcel Proust’s Remembrance of Things Past, wearing a loose dress, with her feet up on a chair and the book in her lap, The Guardian reports.

The portrait is on display at Sotheby’s in London before the auction house’s sale of modern and contemporary works on 1 March.