A decade of dogged detective work has proved that an exquisite terracotta model of Mary holding the body of Christ after his crucifixion was made by Michelangelo, art historians said.

They believe the little statuette was the model for one of the Renaissance master’s most famous works – a white marble statue, called the Pietà, of Mary cradling her son, which he completed in 1499 and is kept today in St Peter's Basilica in the Vatican.

Presenting a new book on their research, art historians revealed extensive documentation from the Renaissance that appears to prove the statue was made by Michelangelo, as well as striking similarities between the object and other, confirmed masterpieces by the artist.

The terracotta piece came to light around 20 years ago, when it was acquired by an antiquarian in northern Italy.

Believing it to be a worthless, kitsch pastiche from the Neapolitan school of art of the 19th century, he kept it in a mouldy box and then sold it to a collector for a pittance.