No one else knows what the pensioner told the priest about what he got up to when he was a naughty altar boy. But his confession holds out the tantalising possibility that there could be a lost Michelangelo on the wall of a village church in Chianti. For centuries the inhabitants of Marcialla have handed down the legend that a fresco above the altar was painted by the great Florentine artist in his youth. And the claim has sometimes been referred to in scholarly texts. But it has recently been learned that, at the end of last year, a stone slab forming part of the altar was heaved aside to reveal the first visible evidence for the claim: a monogram with the letters M, B and F intertwined. MBF is thought to stand for Michelangelo Buonarroti (his name) and fecit (did (it) in Latin), a common way of asserting authorship, or fiorentino (the Florentine). Elsa Masi, a retired chemist and the head of a local cultural association who is leading a campaign to have the fresco examined by experts, told the Guardian yesterday that the M and B were "exactly the same" as in the lettering above a crucifix attributed to Michelangelo in the church of Santo Spirito in Florence. She said the decision to find out what lay behind the altar had been taken by the parish priest, Father Rosario Palumbo, after hearing the confession of an elderly parishioner who said that, during a prank as an altar boy, he had glimpsed the initials. Father Palumbo was not available for comment. Asked about the identity of the parishioner, Ms Masi said: "The priest didn't want to tell me." Stylistic verification of the claim will be difficult because the central part of the fresco was damaged by damp and painted over. But at least one scholar has said there is something of Michelangelo in the muscularity of the thief who stands on the right of the painting Mr Masi said it was plausible that the artist had stayed in or around Marcialla in the tumultuous period after the fall of the Medicis in January 1494. It is known that Michelangelo, a Medici protege, went into hiding at one point and that he had enjoyed the hospitality of the Augustinian order. The church of Santa Maria in Marcialla belonged to the Augustinians until 1570, coming under the authority of the prior of Santo Spirito, who had helped Michelangelo to study anatomy. A succession of diocesan surveys between the late 17th and late 18th centuries stated that the fresco was by Michelangelo, and a scholar of the time, Marco Lastri, noted that it was "said to be by the celebrated Michelangelo". But no one seems to have bothered with the painting again until the 1940s, when two more Italians mentioned the claims. One of them, Roberto Weiss, even ventured an attribution. In a book published in 1942 Weiss quoted an elderly sacristan who said he had been present when a frame around the picture was removed in the previous century. He said the operation had uncovered the letters MBF. A notice was put up in the church recording Weiss's attribution. "Yet no one ever again took an interest in this fresco," said Ms Masi. In part, this may have been because no living person had seen the initials - until last year. Ms Masi said: "If this is attributed to Michelangelo, then all the books that describe his early life are going to have to be rewritten."