Found in a spare room, Fra Angelico works worth £1m

When Jean Preston came across two small panels depicting medieval saints in a box of unwanted items up for a quick sale, she knew they held a special, enigmatic quality.

Miss Preston, from Oxfordshire, was working as a manuscript curator in California, and her art collector father bought them for a couple of hundred pounds in the Sixties to indulge her interest in curious works.

For decades they hung, partly obscured, behind the door of her spare room. It was only after Miss Preston's death, at the age of 77 in July this year, that the panels were found to be key works - worth over £1m - by the Renaissance master painter, Fra Angelico, solving the 200-year mystery of their disappearance.

Yesterday, Dillian Gordon, curator of early Italian paintings at the National Gallery in London, called it a "breathtaking" discovery.

The two pieces, painted in the 1430s, were part of a magnificent altarpiece in Florence that were believed to have been lost, presumably destroyed, during the Napoleonic wars, nearly 400 years after they were created.

Over the years, six of the eight central works of the altarpiece were found, but the whereabouts of the last two remained a mystery. Art experts at Duke's auction house, in Dorset, have estimated the cost of the two 15-inch panels at over £1m, describing them as one of the "most exciting finds for a generation".

The paintings, which depict two unknown Dominican saints, are to be sold at auction in March next year for a "conservative" estimate of more than £1m.

Fra Angelico was originally commissioned by Cosimo De Medici, one of the greatest art patrons of the Italian Renaissance, to create an altarpiece for the high altar at the church and convent of San Marco in Florence, where he lived.

The pieces were found earlier in the year, when Miss Preston was still alive, but the confirmation that they are genuine will cause a stir among the world's collectors of rare Renaissance art. Michael Liversidge, a former dean of the arts faculty at Bristol University, and a friend of Miss Preston, was stunned when he saw the paintings. After careful research, he confirmed they were the missing panels from the altarpiece.

"She knew they were good paintings but had no idea what they were. When I told her the news, she was pleased that her "eye" had been correct," he said.

Guy Schwinge, from Duke's auction house, said that the importance of the discovery could not be over-estimated. He added: "They were intended for his [Fra Angelico's] own church and commissioned by one of the greatest art patrons in history. It simply does not get much better than this. "They are small, but beautifully done and there was some disbelief when we began to tell people what we had come across," he said.

A family member recounted his astonishment when he was told. "My hands shook as I held them, once I realised what they were. To think I was holding the same wood that Fra Angelico picked and painted on some 600 years ago was incredible. Jean bought the paintings because she thought they were rather nice. Someone came in with a box of things they wanted to get rid of. None wanted them but she was a medievalist and actually thought that they were quite nice," he said.

"When I used to stay with her I slept on a sofa bed underneath the paintings. Who would have thought she had the equivalent of a winning lottery ticket in her spare room all these years?"

He added that in spite of owning a number of works of art, including original Pre-Raphaelite works by Rossetti and Watts, which she inherited from her father, Miss Preston lived modestly.

She had been a curator at a museum in California and at Princeton University before retiring in Oxford in 1996. She had bought her clothes from a catalogue, ate frozen meals and travelling by foot or by bus.

The small works are painted in tempera paint on poplar wood with a gold leaf background.

Fra Angelico, which translates from the Italian as the "Angelic One", entered the Dominican order at the age 20 and was described in 1550 by his biographer, Georgio Vasari, as being a "rare and perfect talent". In 1982, he was beatified by Pope John Paul II.

As well as decorating his own monastery, he worked on various other projects, including some at the Vatican in Rome.