A portrait of Lucian Freud, painted by Francis Bacon and not seen in public since it was first exhibited 57 years ago, is to be auctioned at an estimated price of more than 40 million euros (35 35 million British pounds). Sotheby’s said in a press release that  it is the most valuable contemporary work being auctioned in London for almost a decade.

The “Study for Portrait of Lucian Freud” was painted in 1964 and shows Freud with his chest bared and a face monstrous and mangled, sitting on a bench with his arms outstretched and his fists clenched. It is based on a black and white photograph by English photographer John Deakin, a mutual friend of the two artists, and sheds light on a friendship and rivalry that was incredibly intense, but also incredibly bitter.

The painting was the central panel in a triptych exhibited in 1965 in a travelling exhibition to Hamburg, Stockholm and Dublin. With Bacon’s consent, the triptych was broken up with the left hand panel now in a private collection and the right hand one in the Israel Museum in Jerusalem.

Bacon and Freud met in 1944 when they were introduced by the painter Graham Sutherland. They immediately became friends and in the ’50s and’ 60s they saw each other almost every day, both in their studios and eating and drinking in Soho’s most famous haunts. By the 1980s, they had grown apart by petty quarrels and jealousy, with Freud clearly tired of Bacon.

The work has been in the same private collection for 40 years , according to an article by the Guardian and will go on public display at Sotheby’s galleries in New Bond Street London from 23-29 June.

It will be auctioned on 29 June in a sale titled British Art: The Jubilee Season. Other works include Banksy’s portrait of Winston Churchill and David Hockney’s painting of Woldgate Woods.