Hotel Lambert occupies an enviable position on a bend in the River Seine
By David Chazan
BBC News, Paris
It is a mansion fit for a prince - one of the grandest houses in one of the world's most beautiful cities.
But the 17th-Century Hotel Lambert in the heart of Paris is now the focus of a bitter dispute.
French conservationists are taking its new owner, a Qatari prince, to court to try to block his plan to renovate it.
They say it would cause "irreversible damage" to a listed historic monument where Chopin composed some of his music and the writer Voltaire lived with his mistress.
On Tuesday a judge ordered the prince to suspend some of the modernisation work pending a court decision on the conservationists' objections.
Decades of neglect have left Hotel Lambert in a state of disrepair
But the prince, Sheikh Hamad bin Abdullah al-Thani, brother of the Emir of Qatar, insists that the work will restore the stunning but decaying riverside mansion to its former splendour.
From the outside, the Hotel Lambert on the Ile Saint-Louis is a palatial and stately building.
But go inside, and you soon see that the years have taken their toll. Much of the interior is quite dilapidated.
Its former owners, the Rothschild family, sub-divided the building into apartments.
Parts of the timber structure are rotting. The prince's architect has had wooden supports installed to prop it up.
One of the staircases is sagging. Paintings on the ceiling by Charles Le Brun, whose work also graces the Hall of Mirrors in the Palace of Versailles, are cracked and discoloured.
The prince plans to have them restored by French experts.
And he wants to convert the building back into a single residence, scrapping partitions put up when it was divided some 50 years ago.
But members of the Historic Paris association are mounting a legal challenge to the prince's plan because they say it will change the character of the mansion.
"What we object to very strongly is the plan to build an underground car park, install air conditioning and make the external wall about 50cm higher, as well as changes to the facades to return them, supposedly, to the state they were in in the 17th Century," says Pierre Housieaux, head of the association.
But the prince's lawyer, Thierry Tomasi, says the purpose of air conditioning is to preserve the paintings and stop them cracking again.
And he says the underground car park will make it unnecessary to continue parking cars in the courtyard, spoiling the look of the entrance.
The exquisite, but fading, interiors include ceilings by Charles le Brun
Mr Tomasi says the prince is surprised by the criticism of his plans. He says they were drawn up by leading French specialists and "approved and accepted by the French Committee for Historical Monuments".
"The prince is a true lover of French art and architecture, particularly of the 17th Century, of which the Hotel Lambert is a famous example," says Mr Tomasi.
"The very purpose of this project is to preserve the building, to preserve all its elements which have historic, cultural and architectural value and to restore this monument to its past glory."
But some 8,000 people have signed a petition against the work circulated by the Historic Paris association.
Campaigners say the renovation plan goes too far
And the group has enlisted the support of some local celebrities, including a former film star, Michele Morgan, who used to live in an apartment in the building.
"We don't object to the fact that the new owner is a foreigner," says Mr Housieaux, the president of Historic Paris.
"We're grateful that the Hotel Lambert has been acquired by someone who has the means to look after it, but we do oppose his renovation plan because it's too much for this building," he says.
"Renovation isn't about trying to restore the building as it might have been in the 17th Century, it's a question of making do with what's there, keeping the additions made over the centuries and preserving the building."
After buying the mansion two years ago for a princely sum - said to be anything from 60m euros (£50m) - the plan is now to spend another fortune on renovating it.
But until the court case is resolved, this Parisian landmark with its illustrious past faces an uncertain future.