The discovery? The original autograph stock book of Sir Lawrence Alma Tadema, uncovered by the vendor at a clearance auction in the London area and now to be re-offered through Shropshire-based auction house Mullock's at their sale in Ludlow, Shropshire on May 27.
The handwritten, morocco-bound book - which lists everything which both Sir Lawrence and his wife painted in their entire careers - was found in a carton full of 1960s girlie magazines.
"The man who spotted it rang me up and asked me for my opinion as to whether he should bid for it," Mullock's historical documents specialist Richard Westwood-Brookes told ATG. "I told him immediately that what he had discovered was a true art historical treasure and he should try to get it at any price.
"In the end he paid just a few pounds for the whole carton, and then the underbidder asked him if he would sell him the magazines - which I gather he did."
Mullock's are now offering the book with a guide price of £5000-7000.
"For an art dealer or art historian this book is certainly worth that," said Mr Westwood-Brookes.
"Alma-Tadema has listed everything he ever painted and everything which has been attributed to his wife, so this is a definitive record of what is and what isn't an original painting by him.
"Of particular interest are the copious notes which he wrote about both sets of paintings - and also the indication that some of them were overpainted, altered and given different titles.
"There are also details on where paintings were exhibited and who the original customers were."
Alma-Tadema was one of the most significant artists of the late 19th and early 20th in Britain.
He was certainly one of the most famous and highly paid artists of his time, and his commissions, as listed in this ledger, bear witness to this.
Portraits include those of Paderewski, Hans Richter, the Duchess of Cleveland and Joseph Joachim - while customers include the Prince and Princess of Wales, as well as leading galleries and institutions throughout the world.
Alma-Tadema is best known for his classical themes - largely through the inspirations he received when he visited Pompeii as a young man.
At the height of his fame, paintings by Alma-Tadema would sell for £10,000 or more (say £1m plus in today's money). Yet at the end of the Victorian era his popularity faded and his paintings were denounced. Ruskin, for example, dubbed him "the worst painter of the 19th century" - and another critic said that his paintings were "about worthy enough to adorn bourbon boxes".
During this period you could obtain an Alma-Tadema original for as little as £20.
Inevitably however, during the last 30 years his art has been re-evaluated and he is now regarded as one of the foremost painters of classical subjects of his era.
One of his most celebrated works, The Finding of Moses, dating from 1904 (and listed here as having been completed on December 29th of that year) sold at Christie's New York in 1995 for £1.75m.
"It is rare, to say the least, that such an important primary source of information on the works of a leading 19th century artist comes on the market, and in this case it is a most fortunate act of rescue - thanks to an eagle-eyed vendor and a bunch of girlie magazines," said Mr Westwood-Brookes.
Further information from Richard Westwood-Brookes on 01568 770803.
by Ivan Macquisten