Sotheby's cancelled the auction after the collection, amassed by the famous musician and his wife, soprano Galina Vishnevskaya, abroad, had been "acquired privately in its entirety" by a Kremlin-friendly tycoon. The collection was preliminarily estimated at about $40 million.
In an interview on the Ekho Moskvy radio, Alisher Usmanov said he had also paid buyer's premium and commission to the auction house.
The businessman, who co-owns major steel factories, heads a subsidiary of state-controlled energy giant Gazprom, and has invested in media, telecoms and banking, said earlier he would donate the collection, comprising 450 pieces of 18th-19th-century Russian art, to the state.
The collection was built up by the celebrated couple after they were forced to leave Russia in 1974. It comprises of porcelain and glassware, as well as paintings by Nikolai Roerich, Valentin Serov, Ilya Repin and Karl Bryullov. Rostropovich died at the age of 80 in Moscow this April.
Usmanov told the radio channel the collection was still in London, and would arrive in Russia in October.
"We now have a clear understanding of when it will return to Russian soil. This will happen in October, when it will arrive in Moscow or St. Petersburg," the businessman said.
Experts earlier said a museum to keep the collection was being chosen at the moment. They suggested it could be split into porcelain, which could be displayed in the Kremlin museum, and paintings and sculptures to go to museums in Moscow and St. Petersburg.
Also this week, the billionaire increased his stake in Arsenal soccer club to 21% and became its second largest shareholder. In August, he acquired 14.65% in the Premier League club.
In early September, the magnate bought the rights to a collection of Soviet-era cartoons from U.S.-based film company Films By Jove (FBJ) and presented them to Bibigon, a new Russian children's channel proposed by President Vladimir Putin, which started broadcasting on September 1.
