Over the past decade, Russian billionaire Dmitry Rybolovlev shelled out US$2 billion (S$2.8 billion) for 38 pieces of art, building an impressive collection of significant works.
"It is one of the best collections in history. It is remarkable," an art dealer based in New York told The Sunday Times, speaking on condition of anonymity.
Among the pieces is a US$127.5 million Leonardo da Vinci painting, Le Christ Comme Salvator Mundi.
"No private collection has a da Vinci that is as universally accepted as this one. It's like having a unicorn," said the dealer.
Mr Rybolovlev also counts nudes by Italian artist Amedeo Modigliani among his collection. One of them, Nu Couche Au Coussin Bleu, cost him US$118 million.
Likening a Modigliani nude to the Holy Grail, the dealer said: "If you have a Modigliani nude, it's a very special thing because so few people have them. The fact that the collection has three of them is the most remarkable thing. That's about 40 per cent of them in private hands."
Other significant works include Gustav Klimt's Water Serpents II and Paul Gauguin's Otahi, he said.
The collection also boasts works by Pablo Picasso, Vincent van Gogh, Edgar Degas, Claude Monet, Henri de Toulouse-Lautrec, Pierre-Auguste Renoir, El Greco, Auguste Rodin, Aristide Maillol, Henri Matisse, Alberto Giacometti and Rene Magritte.
On the art industry in general, the dealer said that buying and selling of masterpieces are always carried out anonymously.
"Our trade is not paintings. It's information on who are the owners and who are the buyers."