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The painting, by the British artist Alessandro Raho, features the Oscar-winning star standing against a plain white background.

"I was thrilled and very flattered when the gallery said they wanted to commission my portrait," Dench said.

"Alessandro was charming and immediately put me at my ease. It was a pleasure to work with him."

Costume

The artist, who is known for "dressing up" his subjects in theatrical clothes, opted instead to feature the actress without props or a special costume.

Instead he took 200 photographs of her in an hour-long sitting, which served as his inspiration for the portrait.

"I attempted to trap something I saw in her while she waited in the main hall of the National Portrait Gallery, unaware of me," he said.

"To paint a contemporary 'theatrical portrait' was an exciting, and new, prospect," he said. "Of course one also attempts to make the painting engaging even to a viewer unaware of her fame."

The portrait will be on display in Room 40 of the gallery.