It is fitted with an anti-missile system, has a mini-submarine and boasts a 20-metre swimming pool, the largest of any superyacht in the world.
In a statement in 2010, Mr Putin's spokesman Dmitry Peskov said Mr Putin "has never had any relationship to" the $1 billion palace.
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The BBC said it had seen documents from one of the offshore companies that diverted millions of dollars to the palace, which was constructed during Mr Putin’s first term as president.
It said that, according to Mr Kolesnikov, the owner of the company, Lirus Investment Holding, was Mr Putin himself.
He said: “I’m still sure Putin is the richest man in Europe, one of the richest men in the world.” The US Treasury told the BBC it has evidence to tie Putin to profits from a businessman on the US sanctions list, Gennady Timchenko, a long-time Putin acquaintance and then co-owner of Gunvor, which trades nearly 3 per cent of the world's oil.