In a video released today, leading Russian opposition figure Alexey Navalny alleged that a former Trump campaign aide “transmitted” information to the Kremlin. The conduit: Russian aluminum magnate Oleg Deripaska, who is known to be part of Vladimir Putin’s inner circle.

Paul Manafort worked with Deripaska for many years before joining the Trump campaign, and was under FBI investigation as early as 2014. In 2016, while working as Trump’s campaign manager, Manafort reportedly offered (paywall) to brief Deripaska on the Trump campaign.

In a 25-minute Youtube video (Russian with subtitles), Navalny shows footage of Deripaska with Russian deputy prime minister Sergei Prikhodko on his yacht in Norway in August 2016. Based on that footage, he alleges that information about the Trump campaign must have passed between the two.

However, it is unclear if Deripaska took Manafort’s briefings to begin with. When the Washington Post reported Manafort’s offer of briefings in September, Deripaska told CNN it was “fake news.” His spokesman has strongly rejected Navalny’s report. “These scandalous and mendacious assumptions are driven by sensationalism and we totally refute these outrageous false allegations in the strongest possible way,” he told the AP in an email.

Navalny bases his allegations on accounts written by an escort, self-described “sex hunter” Nastya Rybka, who was allegedly one of several sex workers on the yacht. She filmed the trip in an Instagram post, footage of which can be seen in Navalny’s video.

In it, Deripaska sits next to Prikhodko and light-heartedly tells Rybka, “We have bad relations with America. Why? Because Sergei Eduardovich’s [Prikhodko] friend is responsible for them. Her name’s Nuland,” he said, referring to Victoria Nuland, then a senior State department official working on Russia. “Nuland, when she was your age, spent a month on a Russian whaling boat. After that she hates our country.”

Navalny also reads from Rybka’s book, in which she describes pseudonymous figures whose descriptions seem to closely match Deripaska and Prikhodko, discussing secretive “business questions” during a fishing trip. Rybka’s accounts don’t appear to specifically mention Deripaska passing on special information about Trump’s campaign.

Navalny says he was originally skeptical of the idea that Deripaska was Manafort’s backchannel to Putin, but says in his video that Prikhodko is the man “who makes these decisions—there he is cruising on a yacht, and as we can hear in the video, discussing politics with [Deripaska],” he says. “Even Nastya Rybka, the witness of all this, says that fishing is a cover, in fact there were some important informal discussions.”

Manafort allegedly offered Deripaska the private briefings on Jul. 7, 2016. The yacht trip allegedly took place over three days from Aug. 6. Less than two weeks later, Manafort resigned from the campaign under heavy scrutiny of his ties to pro-Russian Ukrainian oligarchs. Manafort has since been charged by special counsel Robert Mueller with twelve crimes, including a conspiracy against the United States.

This isn’t the first time Deripaska’s yacht has gotten a politician in trouble. In 2008, George Osborne, who two years later became Britain’s chancellor, was alleged to have met Deripaska four times on his yacht, in an attempt to secure a £50,000 donation to the Conservative party. Osborne denied trying to furtively channel a donation.

Navalny is a longtime critic of president Vladimir Putin. He has been arrested multiple times for protesting against political corruption, most recently against the upcoming presidential elections, and was personally barred from running in the election.