Last week we reported on a newly-discovered self-portrait by Rembrandt, which is to go on view in London for the first time in November. This week another exciting artistic discovery has been made this time in a museum storeroom in Wales.

The oil painting by Jacob Jordaens, a 17th century Flemish artist and pupil of Peter Rubens, was previously unknown to art historians. Thought to have belonged to the Swansea Museum for nearly 150 years, it was considered a copy and catalogued as unknown 18th century artist. Now, it has been identified by art historian and BBC 1 Fake or Fortune? presenter Dr Bendor Grosvenor as a rare preparatory oil sketch for Jordaens’ ‘Atlanta & Meleager’ and is valued at approximately £3 million.

Dr Grosvenor happened upon the work while trawling the Art UK website and become sceptical of the attribution to an unknown artist. “I’m bit of a nerd when it comes to looking through websites and catalogues… I saw this one and had strong suspicions” he told the Sunday Times. Together with fellow art historian, Jacky Klein, Dr Grosvenor travelled to Swansea to see the painting and learned it had been held in storage for decades. Following restoration work, the painting was sent to the Courtauld Institute of Art in London for expert analysis.

It was at the Courtauld that a vital clue to the work’s true identity was unveiled. A series of merchant’s marks on the back of the painting, which combined the letter A and the coat of arms of Jordaens’ hometown Antwerp indicated that the work must have been created between 1619 and 1621. This led experts including Ben van Beneden, director of the Rubenshuis Museum in Antwerp, to conclude that the work must have been a preliminary canvas for ‘Atlanta & Meleager’ which hangs in the Museo del Prado in Madrid. “It’s a great find. I have absolutely no doubt whatsoever that we’re looking at a quintessential painting by Jordaens”, van Beneden said.