A sketch bought for $30 at a house clearance sale is a 500-year-old masterpiece that could sell for $50 million, say experts

• A Massachusetts man purchased an unassuming sketch of a mother and child for $30 at an estate sale.
• The sketch was found to be a previously unknown work of German Renaissance artist Albrecht Dürer.

A sketch purchased for $30 at a house clearance sale in Massachusetts is believed to be a rare artwork worth as much as $50 million, reports say.

Experts identified the drawing of a mother and child as an original by German Renaissance artist Albrecht Dürer, The Art Newspaper reported.

An unnamed man purchased the sketch in Concord, Massachusett.

The drawing had belonged to the late architect Jean-Paul Carlhain, whose children mistakenly believed it was a 20th-century reproduction of a Dürer.

The buyer casually stored the unframed drawing for two years until Clifford Schorer, a senior partner at the London art dealer Agnews, heard about the sketch's existence and asked to view it.

"It was an incredible moment when I saw the Dürer," Schorer told The Art Newspaper. "It was either the greatest forgery I have ever seen — or a masterpiece."

Schorer believes it "could fetch a record price" for a work by an Old Master.

After an authentication process that lasted two years, leading experts have confirmed the drawing is a previously unknown Dürer, the paper reported.

Scholars pointed to the "AD" monogram inscribed on the work, one of the most famous signatures in art history, which had been written with the same ink used in the drawing.

Secondly, the drawing had been made on paper watermarked with a trident, which was used by Dürer in over 200 known works.

The drawing, which has been titled The Virgin and Child With a Flower on a Grassy Bench (1503), is believed to be a preliminary sketch for his later watercolor, The Virgin Among a Multitude of Animals.

The sketch is on display at Agnews Gallery in London.

The original buyer has been given a $100,000 advance, The Art Newspaper reported, and he will receive a further undisclosed amount when the Agnews sale is concluded.