The first episode, tonight at 9pm, focuses on a previously unknown work by Flemish artist Jacob Jordaens - a pupil of Peter Paul Rubens - discovered in a warehouse in Wales.
Along with co-host Jacky Klein the series uncovers works languishing in museum store rooms. The 17th century Jordaens was found in the collection of Swansea Museum.
Catalogued as a work by an unknown 18th century artist, it is in fact a rare preparatory oil study by Jordaens, dated to c.1620, for one of his best known works, the ancient Greek legend Atalanta & Meleager, which hangs in the Prado Museum in Madrid.
Grosvenor said: “At first glance, this painting looked to be a non-starter. But despite all the over-paint, which was some of the worst I have ever seen, there were glimpses of a great painting fighting to come out.”
The attribution was confirmed by the director of the Rubenshuis Museum in Antwerp, Ben van Beneden, who said: “It’s a great find. I have absolutely no doubt whatsoever that we’re looking at a quintessential painting by Jordaens.”
Grosvenor first saw the work on Art UK, previously called the Public Catalogue Foundation, a database of more than 200,000 oil paintings by 38,000 artists owned by public institutions.
The database, run as a charity, collates the art work of 3,000 public collections online to showcase what is owned by the country.
The current auction record for a work by Jordaens is held by another study of a similar size, Saint Martin Healing the Possessed Man, which sold for $4.7m (£3.6m) in New York earlier this year.