One of the earliest works by the 18th-century Suffolk painter Thomas Gainsborough could fetch up to £50,000 at auction – after originally being bought for just £2,600.

Sudbury-born artist Gainsborough (1727-88) is believed to have painted the portrait of a woman, a member of the Seton family, at the age of 16 while he was lodging in Hatton Garden, London.

The artwork was bought by its current owner, retired company director Robert Mulraine, at auction in 2016 for £2,600 before it was authenticated as being created by a young Gainsborough. Now it has a pre-sale estimate of £30,000 to £50,000.

Mr Mulraine said at the time that he had become involved in searching for misattributed paintings online thanks to his art restorer son, James.

He said he saw the portrait, which at the time was attributed to the circle of painter Arthur Devis, and believed it could be a Gainsborough.

Following extensive research, the work was identified as being by Gainsborough and has since been included in the 2019 publication of art historian Hugh Belsey, catalogue raisonne, as Portrait of a Young Woman in a Green Dress.

Mr Belsey, a Gainsborough expert, said: “It is only in recent years that Thomas Gainsborough’s earliest portraits have been identified.

“The artist’s acute observation and his extraordinary ability to paint fabrics are tell-tale traits and this small portrait of a young woman from the Seton family is amongst the very earliest painted by Gainsborough.

“It has not been possible to establish the precise identity of the sitter… she probably lived in London rather than the artist’s native Suffolk.”

In his authoritative catalogue, Thomas Gainsborough: The Portraits, Fancy Pictures And Copies After Old Masters, Mr Belsey lists only two earlier portraits.

The first is a miniature portrait of a young girl and the second, a self-portrait believed to have been painted by Gainsborough in his early teens, sold by Cheffins auctioneers in Cambridge last year for a hammer price of £90,000.

Nicolas Martineau, of Cheffins – where the artwork is to be sold, said: “This latest and exciting discovery represents a further glimpse into Gainsborough’s early career helping us to fully appreciate his extraordinary ability from an early age.”

The portrait will form part of The Fine Sale at Cheffins on March 23.