A Moscow court has ruled in favour of multibillionaire Alisher Usmanov in his libel suit against Russian opposition leader Alexei Navalny.
Mr Usmanov, estimated to be worth 15 billion US dollars (£11 billion), sued Mr Navalny over his investigation into prime minister Dmitry Medvedev's alleged secret wealth.
The judge at Moscow's Lyublinsky district court ordered Mr Navalny to remove his YouTube documentary about Mr Medvedev's alleged wealth from the web and publish a retraction.
The video has had nearly 22 million views since it was released in March and became one of the most viewed Russian-language videos this year.
Mr Navalny vowed to appeal against the ruling and refused to comply with it.
"You heard the key phrase in the verdict just now, the reason why this trial was held: 'To remove the video and remove the investigation'," he told reporters outside the court. "We are not going to do that. This investigation is based on facts."
Even if he complied, others may have copied the hour-long documentary and could keep it in circulation on the web.
Mr Navalny, who made his name with a blog exposing official corruption, has published legal documents showing that Mr Usmanov and several other Russian billionaires transferred lucrative assets to a charity foundation run by Mr Medvedev's former classmate.
Mr Medvedev has denied any connection to the property while Mr Usmanov has insisted that the transfer of the ownership of a luxury mansion to the charity foundation was a bona fide business deal.
In a two-day trial, the judge dismissed nearly all the motions Mr Navalny filed, including to summon Mr Medvedev to give evidence. She did not allow any witnesses to appear in front of the court or review the documents the investigation was based on.
Earlier this month the reclusive Mr Usmanov released a YouTube video dismissing Mr Navalny as a "loser" and concluded the 12-minute clip with: "I spit on you."
A week later, the 63-year-old tycoon released another angry video, signing off with: "I spit on you again."
Forbes magazine earlier this year listed Mr Usmanov as Russia's fifth-richest man. Earlier this month, Britain's Sunday Times published similar estimates.
Street protests in dozens of Russian cities and towns in March, triggered by the investigation, were some of the most widespread in years.
Mr Navalny has called for more protests on June 12, and activists in about 200 cities and towns have applied for permission to rally.
Mr Navalny said on Wednesday that the verdict in Mr Usmanov's favour should bring even more people to the streets at the protests.