A PAINTING which lay undiscovered for years in a County Durham museum will be revealed as a £1m masterpiece this weekend.

Art experts have identified a 17th-century portrait by King Charles I’s court painter Sir Anthony Van Dyck after it was spotted on a website by Dr Bendor Grosvenor, an art historian and dealer.

The portrait, which dates from the 1630s and measures around 72cm by 61cm, is of Olivia Boteler Porter, who was a lady-in-waiting to Henrietta Maria, the wife of King Charles I.

It has been kept for years in The Bowes Museum, in Barnard Castle, where it was thought to be a copy after Sir Anthony Van Dyck and not usually put on show.

But Dr Grosvenor saw it after it was uploaded to the BBC Your Paintings website as part of a 10-year project to make the national collection of oil paintings available online.

Tonight (Saturday, March 9) the BBC2 programme Your Paintings: A Culture Show Special follows Dr Grosvenor and presenter Alastair Sooke as they restore and re-examine the painting to identify its history.

Dr Grosvenor said: “To find a portrait by Van Dyck is rare enough, but to find one of his friendship portraits like this, of the wife of his best friend in England, is extraordinarily lucky."

He added: “Had it appeared at auction as a copy, and in its dirty state, it would probably only have been estimated at about £3,000 to £5,000.

Adrian Jenkins, director of The Bowes Museum, said: “This is a thrilling attribution for The Bowes Museum and the end of a chain of events that began with the photography of the entire collection five years ago for the Public Catalogue Foundation.”

* Your Paintings: A Culture Show Special is on BBC2 at 6.30pm tonight.