The prince, the PM and the Mona Lisa

Blair's aristocratic Tuscan friends are said to be direct descendants of Leonardo's most famous subject

Two Tuscan beauties have given a tantalising clue as to why Tony Blair cannot resist returning to the hospitality of Prince Girolamo Guicciardini Strozzi outside San Gimignano.

The home of the prince, a professor of international law, has a swimming pool and tennis court, and the estate is comfortingly buried in dense woods.

But perhaps what really keeps the Prime Minister coming back are the enigmatic yet strangely familiar smiles radiating from the prince's two charming daughters, Natalia and Irina. Because now an Italian genealogy expert, Domenico Savini, has revealed that the Strozzi family descends directly from Lisa Gherardini, otherwise known as Mona Lisa.

"It's a matter of great emotion and great pride to learn that we are descended from La Gioconda," said Natalia Strozzi, 30, an actress. The subject of Leonardo's most famous painting is known as "La Gioconda" in Italy. "We had a vague knowledge of this family story, but the fact that it's been documented proves that it is true, which makes us take it more seriously." And what about the celebrated smile? "Yes," she went on, "once in a while a smile like that flits across our father's face, and that's the most convincing proof there is."

Italian researchers have been closing in on Mona Lisa in recent weeks. Not only have her descendants (by the female line) been identified in the Strozzi family, but one of the most tenacious Leonardo researchers, Giuseppe Pallanti, claims to have unearthed church documents proving beyond doubt where she lived and died.

Professor Pallanti told a press conference in Florence that he had discovered that the remains of Lisa Gherardini are buried in the ruins of a convent in Florence, Convento di Sant'Orsola.

Signora Gherardini moved into the convent, where her daughter was a nun, when her own health began to fail after her husband's death in 1538. She died four years later, on 15 July 1542, at the age of 63, 39 years after her portrait was painted.

It did not take long for Professor Pallanti's researches to be politely rubbished: Mona Lisa studies is an acrimonious field. But definitive proof may not be far away. A Tuscan engineer famed for his detective work on great paintings has offered to root round under the convent for Lisa Gherardini's remains.

If they were found, it would not be beyond modern technology to reconstruct her appearance and settle the question of whether she was the true Mona Lisa once and for all.