A painting bought years ago by a priest for about $650 at an antiques shop, and thought to be a copy, was recently identified as an original Anthony van Dyck portrait.

The work, which hung on the wall of Father Jamie MacLeod's home for more than a decade, has been valued at $650,000 after he brought it into the "Antiques Roadshow."

It is the most valuable painting to be identified in the 36-year history of the program, reports the Irish Independent.

Father MacLeod purchased the painting over 12 years ago from a now closed Cheshire, England antiques shop. When he took the painting to a roadshow in Newstead Abbey, near Nottingham, "Antiques Roadshow" host Fiona Bruce, who was making a show about van Dyck with expert Philip Mould, saw the work and wondered whether it was genuine.

After weeks of cleaning and the removal of a top coat of 18th century paint, the work was verified by Dr Christopher Brown, a leading authority on the Flemish artist, who was a leading court painter in England under Charles I.

Father MacLeod, who helps to run a retreat house in Whaley Bridge in England's Peak District, plans to sell the the rare painting to buy new church bells.

"It's been an emotional experience and it's such great news," he said.

"It's wonderful that new church bells hopefully will be pealing out to commemorate the centenary of the end of the First World War in 2018."

Bruce said, "It's everyone's dream to spot a hidden masterpiece, I'm thrilled that my hunch paid off. To discover a genuine van Dyck is incredibly exciting. I'm so pleased for Fr MacLeod."

The painting discovered on the show is a portrait of a magistrate of Brussels and is believed to have been painted as part of the van Dyck's preparation for a 1634 work showing seven magistrates, which was eventually destroyed in a French attack on Brussels in 1695.

"Discoveries of this type are exceptionally rare," said Mould. "The painting's emergence from beneath layers of paint was dramatic.

"It's been revealed as a thrilling example of van Dyck's skills of direct observation that made him so great a portrait painter."