Two self-portraits by the renowned British artist Francis Bacon have been discovered in a private collection, and will go up for sale at Sotheby’s London Contemporary Art Evening Sale on July 1.

Self Portrait (1975) and Three Studies for Self-Portrait (1980) are estimated to fetch £15 million each.

‘Apart from being reproduced in books they’ve not been seen’, Oliver Barker, Sotheby’s senior international specialist in contemporary art, said.

Marlborough Fine Art, who were Bacon’s main dealer, kept an archive of his work, so there was a photographic record of the paintings. They were also were reproduced in a book of Bacon’s self portraits, which Barker describes as ‘pivotal’ to his questioning of human existence.

The decision of the descendants of the original collector to sell means that they will be seen in public for the first time in 40 years.

“We knew of the existence of the paintings but simply had no idea where they could be.” Barker said. “The first time I saw these paintings it was such a wonderful awakening. They’re both so luminous.”

Bacon broke records in 2013 when his triple portrait of fellow artist Lucian Freud fetched £89million at Christie’s, making it the most expensive artwork ever sold at auction.

It is a good time for fans of Bacon’s work. Francis Bacon & The Masters at the Sainsbury Centre for Visual Arts in Norwich provides a rare opportunity to see his work alongside many of the Old Master painters that inspired him. Including many masterpieces from the Hermitage in St. Petersburg, it features a core of 13 paintings by Bacon that Robert and Lisa Sainsbury collected during Bacon’s lifetime, and is on view until July 26th.