THE Flemish Baroque artist Sir Anthony van Dyck was a child prodigy whose fame was established by the time he was 16. Born in 1599, he moved to London in 1630, quickly becoming King Charles I’s favourite painter.

He died in 1641 and more than 200 years later, John and Josephine Bowes, who were in the process of developing a museum and art gallery in a grand French chateau-style building on the outskirts of Barnard Castle, bought two pictures – described as in the style of van Dyck – in Paris for 45 francs.

One was thought to be a portrait of Charles I’s wife, Queen Henrietta Maria.

Although it had been in the Bowes collection since the museum opened in 1892, it had languished unseen and overlooked due to its poor condition.

And it may have remained locked away had it not been spotted by art sleuth Dr Bendor Grosvenor.

The picture – along with more than 200,000 others – was photographed and placed on the Your Paintings website, set up because there is not enough wall space in Britain’s galleries to display all publicly-owned art.

Dr Grosvenor, a fan of van Dyck, believed he had stumbled across an original and his investigation into proving its authenticity enthralled an audience of millions who tuned into BBC2’s Culture Show recently.

“I think it’s by the man himself.

If you spend a lot of time looking at the real thing and lots of copies, you soon begin to see the difference – you get a feel for these things,” he said in the early stages of the programme.

So the inquiry began to see what really lay behind nearly 400 years of grime and varnish.

First stop was Libby Sheldon, art historian at University College London, whose work on the pigments used in the paint proved the picture dated from the 17th century, ruling out the possibility it was a later copy.

This was a major breakthrough, as van Dyck’s style was emulated by artists for centuries after his death.

She declared there was nothing to say the picture wasn’t by van Dyck, but more work was needed to prove it was the work of the celebrated artist.

Next came a visit to the National Portrait Gallery to establish exactly who was the subject of the portrait.

After discounting several possibilities, Dr Grosvenor came up with Olive Boteler Porter, the queen’s lady-inwaiting and wife of van Dyck’s friend and patron, Endymion Porter. Olive was the daughter of Sir John Boteler and Elizabeth Villiers, niece of the Duke of Buckingham, and while in England, van Dyck painted a number of portraits of members of the family.

Confirmation came after Dr Grosvenor got in touch with Olive’s descendents, who showed him another portrait of her – and the two matched.

Specialist restorer Simon Gillespie was then engaged to remove the dirt and old varnish from the picture and restore Olive to her former glory.

Finally, after weeks of painstaking restoration work, the painting was shown to Dr Christopher Brown, director of the Ashmolean Museum, in Oxford, and the country’s leading authority on van Dyck.

He said that due to the artist’s fame and the large number of copies and paintings produced in his style, about nine out of every ten shown to him turned out not to be the real deal.

Not so in this case.

“It is quite clear this is a late English period van Dyck, “ he said. Describing the work as elegant, he added: “This absolutely is van Dyck at his best. It is a substantial discovery.”

Not surprisingly, Portrait of Olive Boteler Porter is no longer languishing unloved in the Bowes Museum’s store but is now a front-ofhouse star.

Officials hope the fascinating detetctive story as revealed on national television will lead to a surge of interest, not just from regular visitors in the North-East, but among art lovers nationally.

Museum director Adrian Jenkins said the impact of the programme was already being felt, with headlines at home and abroad and a surge of interest on social media.

“We have received a huge number of inquiries about the painting and have already had visitors coming specifically to see it on display,”

he said.