After more than a century collecting dust in a storeroom, a painting owned by the Queen has been unveiled as a work of Italian master Caravaggio, royal art officials said Friday.

The painting, now identified as The Calling Of Saints Peter and Andrew, is one of about 50 surviving works by the Renaissance master.

"It's a huge addition to the collection," said Desmond Shawe-Taylor, surveyor of the Queen's pictures.

Originally thought to be only a copy of a lost masterpiece because of its accumulated layers of dust, the painting underwent a restoration after analysis in 2000 led scholars to believe it might be an original.

"The dirt, old glue, and varnish layers obscured the details and the painting appeared almost monochrome, in varying shades of brown … It looked like nothing," Shawe-Taylor said.

A copy of a painting usually has an outline of the picture on the canvas for X-ray and infrared investigation did not reveal any such markings.

The picture was purchased by King Charles I in the 17th century and had been resting in a Hampton Court Palace storeroom for years.

Painting cannot be sold

The uncovered painting, one of 7,000 in the Queen's collection, is said to be worth $108 million. However, the Queen cannot sell the painting because under British law she acts as a holder of the Royal trust on behalf of the nation.

A source told London's Daily Telegraph that Queen Elizabeth has taken "a keen interest in the conservation department and has been aware that this examination has been going on" but may have been unaware of the final results.

The painting will be featured in a Caravaggio exhibition opening in Rome on Nov. 21 before joining an exhibition of Italian Baroque and Renaissance art opening at Buckingham Palace in March.

Michelangelo Merisi da Caravaggio (1571-1610), considered the first modern artist for his realism and use of light and shadow as a painter, also had a reputation as a hotheaded rebel and was known for his drinking and duelling.

With files from the Associated Press