French dealer Yvon Lambert, 75, will donate his personal art collection to the French state, according to reports in L'express and Artinfo.com. The announcement was made on Nov. 18, during Nicolas Sarkozy's visit to the Lambert Collection in Avignon, in the south of France.

Since 2000, Lambert's collection has been on loan to the city of Avignon, where it has been housed in an 18th-century mansion, the Hôtel de Caumont. The deal was almost scrapped last year, when Lambert, unhappy with the damp conditions there and apparent indifference on the part of the mayor's office, threatened to remove his collection from the facility.

The donation is considered the most important gift of art to the state since that of the Picasso estate in 1974. With 450 works by such artists as Christian Boltanski, Robert Ryman, Jean-Michel Basquiat, Cy Twombly, Andres Serrano, Sol LeWitt, Anselm Kiefer, Nan Goldin and Douglas Gordon, the collection is estimated to be worth $120 million. It is currently being appraised by Christie's.

As part of the arrangement, the collection will expand into a neighboring mansion by 2015, giving it twice as much exhibition space.

The gift is similar to that of London dealer Anthony d'Offay, whose collection was acquired in 2008 by the U.K. as a partial gift/partial sale at cost. The works have been used to establish "Artist Rooms" that rotate among U.K. institutions.

In April, Lambert shuttered his New York gallery and turned over management of his Paris space, which he founded in 1967, to director Olivier Bélot.