A new picture by Leonardo da Vinci has been discovered, the National Gallery in London has said.
It said experts using infra-red techniques found a drawing under the surface of the Virgin of the Rocks painting which hangs at the gallery.
It believes the drawing shows a woman kneeling with one arm stretched out.
Experts believe the Italian Renaissance painter was planning a picture of an adoration of the child Christ but abandoned the idea.
Leonardo was commissioned to paint the Virgin of the Rocks to decorate an altarpiece in a chapel in Milan in 1483.
The artist appears to have painted two versions.
One, which now hangs in the Louvre, was probably sold to a private client, says BBC arts correspondent Rebecca Jones.
The other, which hangs in the National Gallery, was placed in the chapel in 1508.
It is under this painting that experts believe they have found a drawing of a kneeling woman.
She is pictured with her eyes downcast and one of her hands stretched out.
Experts think Leonardo da Vinci was probably planning a picture of an adoration of the Christ child, but abandoned the idea before drawing Jesus as a baby, our correspondent says.
However, why he painted over the work may never be known, she adds.
The Virgin of the Rocks was the first painting executed by Leonardo after his arrival in Milan.
Critics have argued over exactly what the painting depicts.
Some claim it shows the Immaculate Conception, while others believe it recalls the moment when the infant Christ met St John the Baptist.
Leonardo painted the Mona Lisa, considered to be among the world's most famous paintings.
His other masterpieces include the Last Supper and Adoration of the Magi.