A 25-by-30-inch oil painting called “Country Fair” was mistakenly sold at a tag sale in Thornwood last month.

Helen Giustino, 88, says she acquired the painting with her late husband from a flea market over 30 years ago.

“It was something my husband loved. It was a flea market, he loved flea markets, that was part of our entertainment through our years,” says Giustino.

The widow’s son sold the piece for a mere $200. Turns out it is valued at nearly $30,000. She says she is angry and emotional to know that the piece is gone.

The painting, which was featured in a 1947 Maxwell House ad, was scheduled to be auctioned off at the end of November.

Ronnan Clarke, owner of Clarke's Auction Gallery in Larchmont, intended to keep 10% of the sale and give the consignor, Dr. Sidney Hiller of Briarcliff, the rest.

Hiller says he plans to take the painting back from the auction house and pursue ownership. He declined to comment on whether he would return it to the original owner.

Giustino’s attorney, John Murtagh, says the family is prepared to take legal action.

“The right, ethical, equitable things to do would be let's everybody go back to square one, give Helen back the painting that means so much to her, we can give him back the $200 he paid for it and this is over and done,” says Murtagh.