Photo: Detail from the fourth panel of Botticelli's Story of Nastagio degli Onesti

Thanks to a last-minute decision by the bearer of one of the most illustrious names in fashion, a long unseen Botticelli is to be unveiled to the public tomorrow at what the organisers say is the biggest exhibition to date of the painter's work. Thirty of the Florentine artist's paintings will feature in a display at the Palazzo Strozzi in Florence until July 11. Among them is the Mystical Nativity, which the National Gallery in London only lent on condition that it be insured for a record sum of £35m. The never previously displayed masterpiece, however, is the last of four panels that make up one of Botticelli's most disturbing works - The Story of Nastagio degli Onesti. Behind the story of its re-emergence is a tale of two celebrity marriages, both celebrated in Florence, almost 500 years apart. When the fashion designer Emilio Pucci announced his engagement to Cristina Nannini in 1959, he declared he was "going to marry a Botticelli". Indeed, his marriage seems to have moved him to design one of his most celebrated print series, infused with motifs borrowed from the Renaissance master. But Pucci's ancestors had had an earlier involvement with Botticelli.

In 1483 Gianozzo Pucci was preparing to marry. His uncle, Lorenzo Medici, commissioned the painter to bring alive a story from the Decameron, the 14th-century masterpiece written by Giovanni Boccaccio. Pointedly, in the circumstances, it suggests a dreadful fate awaits women who reject the entreaties of decent young suitors. The four panels making up the work remained in the Pucci family until 1868. Three were later bought by the Catalan statesman Francisco Cambó, and donated to Madrid's Prado Museum in 1941. The fourth and last panel disappeared from public view and many believed it had ended up in a private collection in the US. But the curators of the Florence exhibition, who succeeded in persuading the Spanish to lend them the third panel in the series, discovered the fourth was not on the other side of the Atlantic, but a mere a quarter of a mile from the Palazzo Strozzi. Having been bought at auction by the late Emilio Pucci at the height of his Botticelli phase in the 60s, the painting was tracked down to the home of his widow Cristina. "The organisers and authorities requested the work and did not receive any reply," Jonathan Nelson, a co-curator of the exhibition told the Guardian. Last month a story appeared in an Italian newspaper criticising the Puccis for not lending their panel. "Immediately after that article came out, the marchioness got in contact and now the work is going to be shown," Prof Nelson said. Cristina Pucci said in a statement the delay was because of a "simple misunderstanding". The panel was expected to be delivered to the exhibition last night. "No one has seen it, including myself," Prof Nelson said. "All the reproductions of it are old. Normally, in books, you see three beautiful works and then one lousy one." The Story of Nastagio degli Onesti is central to the theme of the exhibition, which also includes works by Filippino Lippi and is subtitled Passion and Grace in 15th-century Florentine painting. Prof Nelson said the display hoped to show that the artist was "not only a painter of graceful half-naked women dancing in fields, but also a painter of very dramatic, and violent, images".John Hoper, Rome/GuardianNewsWire.