ESSEX, U.K.- An early portrait by artist John Constable has been discovered and is due to be sold by Sotheby's, the auction house has said. The painting, The Daughters of Mr. W Mason of Colchester, is due to go under the hammer on  June 13, and is expected to fetch between £50,000 and £80,000. Its existence was previously unknown to art historians. The Mason family lived in Jupe's Hill, in Dedham, near Colchester, Essex - the neighboring village to East Bergholt, the artist's birthplace. Mr. Mason was the artist's lawyer, and the portrait is believed to have been painted in lieu of payment of a debt. It then passed through successive generations of the family. It was found by a fine art valuer during a routine valuation at an unidentified house in East Anglia. The find was authenticated by Graham Reynolds, one of the country's leading Constable scholars, Sotheby's said.