The sale took place back in October, but only now does David Glasser, chairman of the London Jewish Museum of Art, (also known as the Ben Uri Gallery) feel able to talk about the sale.
The work in question is a surrealist painting by Russian-French artist Marc Chagall, regarded as one of the key figures of 20th century art. The 1945 piece, Apocalypse in Lilac, Capriccio, depicts the crucifixion of Christ with a Nazi official skulking below.
The work - perhaps a sarcastic comment on the failure of some to see Nazism's incompatibility with Christianity, despite Jesus being Jewish - is one of a handful of works depicting Christ (as a Jew) during WW2, and none of these has previously been held in the UK.
On discovering the work, which despite being correctly listed had a surprisingly low estimate in the Paris auction, the museum simply kept quiet about it and bid with as little fuss as possible.
(It can be expensive if you show too much enthusiasm at auction and encourage the auctioneer to employ techniques such as 'taking bids off the wall', as we explained in our guide to auction bidding in a recent newsletter.)
The museum had been backed by the British Art Fund, strengthening its financial clout, but nevertheless it would not have felt confident bidding against major French institutions. In the event, the Art Fund's assistance was not needed and they picked up the work for €30,000. The work has been valued by various experts around the world as worth 10 or 20 times that amount.
But Glasser was still not confident of acquiring the work, as he thought an export licence might be refused if France Museum of Modern Art objected. Only now he has received the work is he prepared to tell the story.
Apocalypse in Lilac, Capriccio, will be on view in the Osborne Samuel gallery in Mayfair, London, this week. Collectors interested in 20th century art and artists may want to take a look at this photograph of Damien Hirst's For the Love of God (a diamond skull) signed by the artist.