Seated Figure (Red Cardinal) has been known to experts only from a black- and-white photograph and has not been seen by the public for 35 years. Its sale at Christie's on 4 December - for an estimated pounds 1.5m - is hailed as a return to confidence in the art market.
Bacon painted Seated Figure in 1960. It resided in an American collection until the 1970s, and was then bought by a European collector.
Bacon died in April 1992; a new biography by Michael Peppiatt, Anatomy of an Enigma, details the artist's love affair with Peter Lacy, and tells how many of his works were destroyed.