Painting that sellers insist is by 17th-century master is to be sold after being found in attic

Sellers of a painting that they insist is a lost Caravaggio and worth in excess of £100m have announced it will be sold this summer without a reserve.

The large painting of Judith beheading Holofornes was found by accident in a Toulouse attic in 2014. It has been pored over by art history experts and scientifically analysed and a highly convincing case has been made that it is from around 1607 and by Caravaggio.

But it is a compelling case rather than a categorical one and that presents a dilemma. “The poor buyer of this picture will not enjoy it,” said Eric Turquin, a Paris-based expert in the Old Masters. “He will have to have a special mailbox for all the emails.”

Turquin was in London, accompanied by the painting, to make the case for it being a genuine Caravaggio as it went on display in London.

It was discovered by the auctioneer Marc Labarbe in 2014 during a clearout of an attic in a large house in Toulouse. The painting was kept a secret for two years, with Turquin hanging it in his bedroom despite whom he described as “my poor wife”.

In 2016 the French government placed an export ban on the painting to allow investigations and time for the Louvre to consider whether it should be bought. The museum decided not to buy it but Turquin said that did not mean the work was not a Caravaggio. He said the price of €100m represented 15 years of the Louvre’s acquisition budget in one go, and the museum already had three exceptional Caravaggios.

The Louvre decision opens the door for its auction on 27 June in Toulouse. It has an estimate of £90m to £140m.

Turquin said it would be sold. “It will be an auction without reserve. It will be a real sale, no guarantees, no nothing, a real auction. We have had a lot of interest in the painting and who knows what this painting is worth.”

Facebook Twitter Pinterest Detail from Judith Beheading Holofernes. Photograph: Cabinet Turquin

There are 68 known paintings by Caravaggio, only four of which are in private hands. Turquin said it was “not a picture for a drawing room or a dining room”, and suggested that a museum would be the likely buyer.

The painting depicts the biblical story of Judith, a young widow in the city of Bethulia who puts an end to the Assyrian siege on her city by seducing and beheading the general Holofernes. Looking on is her elderly and clearly ill servant, Abra.

Labarbe said burglars broke into the house where it was found several years earlier but left the painting, believing it worthless.

There are gaps in the story of the painting but Turquin said a good reason for that was because “Caravaggio as an artist was totally out of fashion from 1650 to 1950. His paintings were worth nothing, nobody was looking for them.”

He pointed to the last Caravaggio auction in 1971 when Christie’s put up for sale Martha and Mary Magdalene, which had been discovered in South America. Turquin said the then head of the National Gallery, Michael Levey, did not believe it was a Caravaggio and it failed to sell. Soon after it was bought privately for the Detroit Institute of Arts. “Today there is not one Caravaggio show without a letter sent to Detroit,” said Turquin.

The Judith beheading Holofornes painting will go on display at the Colnaghi gallery in Mayfair, London, between 1 and 9 March.