Two rare self-portraits by Francis Bacon never shown in public before will go under the hammer for the first time at Sotheby’s London Contemporary Art Evening Sale, on July 1.

Bacon’s Self-Portrait and Three Studies for a Self-Portrait were sold directly from the London gallery Marlborough Fine Art soon after they were painted, in 1975 and 1980, respectively. The artworks have a presale estimate of £10-15 million each.

It will be the first time that two self-portraits by the Irish-born artist are offered in the same auction. In 2007, a Bacon self-portrait from the same private collection sold at Sotheby’s for a whopping £21.6 million, which is still the record for any self-portrait by the artist.

Last February, another Bacon self-portrait, the diptych Two Studies for Self-Portrait (1977), sold at Sotheby’s London for £14 million (see Francis Bacon’s Two Studies for Self-Portrait Diptych Estimated To Sell for $27 Million).

The market for Bacon’s fascinating and tortured paintings seems to keep going from strength to strength. Last summer, a small Bacon triptych sold for a £29 million at Sotheby’s London (see Small Francis Bacon Triptych Sells for $45 Million at Sotheby’s London). In 2013, Three Studies of Lucian Freud (1969) shattered records when it sold for £92 million at Christie’s, becoming the most expensive artwork ever sold at auction.

The rare Bacon self-portraits have resurfaced as part of a private collection assembled during the 1970s and 80s that will hit the auction block in a series of sales in Sotheby’s across its branches in London, New York, and Paris between May and July 2015.

Besides the Bacons, the collection includes masterpieces running the gamut from African to contemporary art, all of them focused on the theme of the human figure.

From terracotta heads from Nigeria and Ghana to works by masters like Edgar Degas, Edouard Vuillard, Yves Tanguy, Henry Moore, and Lynn Chadwick, the collection explores 400 years of art looking at the human form.

Crucially, the majority of works from the collection have not been seen in public since they were acquired over thirty years ago.

“I’m extremely excited that Sotheby’s is handling this collection, spearheaded by key works by British artists in two and three dimensions,” Oliver Barker, Sotheby’s senior international specialist in contemporary art, said in a statement. “This sophisticated, focused collection has been quietly enjoyed by its owners for many decades. Hidden away from the public eye, it has resolutely stood the test of time,” he added.