A Francis Bacon triptych, Three Studies for a Portrait of George Dyer, will feature in a sale at Sotheby's London on June 30.
The lot is valued at £15m-20m ($25.1m-33.5m). Oliver Barker of Sotheby's told the Guardian: "Dyer was one of the great loves of Bacon's life and this is the first time a triptych of him has ever come to market.
"The first time I saw it was like uncovering a long lost jewel".
The two men met when Bacon caught Dyer, a petty criminal, attempting to burgle his flat in 1963. They began a torrid love affair, marred by heavy drinking and violence, which ended with Dyer's death from an overdose in 1971.
He is a regular figure in Bacon's work, with one portrait setting a new record for a single canvas by the artist when it sold for £42.1m ($70m) at Christie's in February.
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