A painting brought into the Tankerton branch of auctioneers Bonhams, which turned out to be an Old Master worth millions of pounds, was auctioned yesterday.

It fetched a price of almost £3m - the catalogue for the sale at Bonhams’ New Bond Street sale in London had estimated it could go for between £2m to £3m.

The anonymous owner was left the picture - along with several others - by his uncle and with no room to hang them decided to sell the lot. But one of them was a previously unknown masterpiece by Velazquez.

The amazing story came out in October when the small portrait was unveiled at the London headquarters of Bonhams.

The painting was one of 12 pictures, mostly portraits, brought in to the company’s branch in Tankerton Road last year. They were all thought to be the work of the obscure 19th-century British artist Matthew Shepperson and were valued at £200 to £300 each.

The regional valuer in Whitstable sent them to the Oxford office used for selling lower-value works where Lizzie Hill, director of the pictures department, noticed something different about the portrait of an elderly bald man with a goatee beard.

The Old Master paintings department in London said it should be withdrawn from the sale and sent for closer examination. The specialist said it was an Old Master and Velazquez was the obvious candidate because of the technique and the style and period of the dress.

The last Velazquez to come up for sale was a picture of a female saint which sold for £8.5 million in 2007. The painting was subjected to several tests and all suggested it was the work of Velazquez.

Analysis by the Prado gallery in Madrid, home to half of the artist’s surviving works, supported this view.

Andrew McKenzie, Bonhams’ director of Old Master paintings, said: “The owner lives in a small flat in the Home Counties and inherited this from his uncle. For him it’s going to be a life-changing event.”