Sotheby’s will sell a Francis Bacon diptych Studies of Isabel Rawsthorne, 1983, (detail below, est £1.5m-£2m) at its evening sale of contemporary art on 12 October. Rawsthorne was an artist, one of Bacon’s closest female friends and his nurse in his later years. She was also a model for Derain, Giacometti and Picasso, and Bataille’s girlfriend before marrying the composer Alan Rawsthorne in 1951. After she died in 1992, Bacon revealed in Paris Match that many years before he had had an affair with her. (It was considered a surprising admission as Bacon’s other sexual relationships were believed to have been exclusively with men.) Bacon painted numerous portraits of her, but only three of these diptychs survive.