Gazing into the middle distance, the faintest hint of a smile on her lips, Cecilia Gallerani is a picture of civility. But 500 years after the Duke of Milan's mistress was immortalised by Leonardo da Vinci as the Lady with an Ermine, she is causing major embarrassment for the National Gallery, as the portrait's owners question whether the museum can be trusted to look after her.
The 15th-century masterpiece, considered by experts to be as important as the Mona Lisa, is due to appear in London in November as part of a major exhibition of Leonardo's work. Curators are billing the blockbuster, which is selling out, as "the most complete display of Leonardo's rare surviving paintings ever held". Seven works have been loaned from around the world.
But after an appalling breach of security at the National Gallery last weekend, when a vandal daubed two paintings by Poussin with red paint, the Polish prince who owns the painting is reconsidering its loan. Prince Adam Karol Czartoryski, who is a first cousin of the King of Spain, inherited the work in 1991, and immediately founded the Czartoryski Foundation to safeguard its future. Lady with an Ermine usually hangs in the foundation's museum in Krakow.
Two weeks ago, the prince sensationally dismissed the trust's entire board, including his first cousin, the London-based historian Count Adam Zamoyski. It is understood the prince felt he was losing control of the trust.
Olga Jaros, who took over as chairman of the foundation, confirmed that a decision had yet to be made, and that a contract has yet to be signed with the National Gallery. "In the light of what happened last weekend at the National Gallery, I have informed the foundation what has happened. We are still in negotiations."
Even before Saturday's attack, concerns had been voiced over the painting's hectic schedule. It is at present on loan to the Palacio Real in Madrid for an exhibition of Polish art treasures. It is then scheduled to visit Berlin before travelling to London.
Last November, when the loan to the National Gallery was announced, leading Polish art historians appealed for the painting not to travel. Joanna Daranowska-Lukaszewska, of the Association of Art Historians, wrote a letter saying that, although the picture is insured for ¤300m, "in the event of a disaster, no one would be able to restore this priceless masterpiece ... Lady with an Ermine is the common property of the whole cultural world." Ms Jaros confirmed that the painting is extremely fragile.
The exhibition in November will in the Sainsbury Wing of the National Gallery. To avoid over-crowding, only 180 visitors will be allowed in every 30 minutes. Lady with an Ermine always sits in a protective glass-fronted case. However, cuts at the gallery have brought reductions in staff numbers, and some now have to monitor two rooms.
On Friday, a 57-year-old man was detained under the Mental Health Act following the vandalism of the Poussins. A spokesman for the National Gallery played down suggestions that Lady with an Ermine might not be loaned to London.
"In regard to the Cecilia Gallerani painting, there is no change," she said. "The National Gallery is very pleased to work with Olga Jaros, the newly appointed chairwoman of the Czartoryski Foundation, on the loan painting of Lady with an Ermine.
"The security of the collection is of paramount concern to the National Gallery. The gallery's security arrangements are in keeping with those of other major national and international galleries and museums. Our arrangements have been approved by the National Security Advisor for museums as appropriate for the protection of the collection."
Leonardo da Vinci's most famous painting, the Mona Lisa, never leaves the Louvre in Paris.