Despite the false claim, the disinformation plot was successful.

It took off online and was echoed by members of the US Congress making crucial decisions about military spending.

It was an incredible assertion - using two advisers as proxies, Mr Zelensky paid $75m (£59m) for two yachts.

But not only has the Ukrainian government flatly denied the story, the two ships in question have not even been sold.

On X, formerly Twitter, Republican Congresswoman Marjorie Taylor Greene said: "Anyone who votes to fund Ukraine is funding the most corrupt money scheme of any foreign war in our country's history."

She linked to a story containing the yacht rumour.

While discussing budget priorities on a podcast hosted by former Donald Trump adviser Steve Bannon, Mr Vance said: "There are people who would cut Social Security, throw our grandparents into poverty, why?

So that one of Zelensky's ministers can buy a bigger yacht?"

Although the yacht rumour is false, the BBC has discovered the story was given a major boost by a Russia-linked website that pretends to be located in Washington.

It is, researchers say, a "likely purpose-built tool for narrative laundering with links to the Russian government".

"Narrative laundering" needs to be popularized as a term and concept people recognize. Easiest way for any political party to manipulate a population. Invent credible-looking sources, use them as sources for supposed stories — directly or masking them further through a chain of such sources — and then use that as political rallying points. It's Russian in this case but would be just as effective (or even more so) if home grown. You could argue this was precisely Trump's use of FOX News, particularly the now proven involvement of figures like Sean Hannity and Tucker Carlson.

The story first emerged in late November on an obscure YouTube channel - one with only a handful of followers and just a single video in its feed.

The next day, it was picked up by a site called DC Weekly, alongside pictures of the two yachts - called Lucky Me and My Legacy - and documents purportedly confirming the sale of the boats to Zelensky's associates.

But the luxury yacht brokers where both vessels are listed for sale said that the allegations are false.

The sales documents appear to be forgeries.

And instead of having been purchased by Zelensky or his close advisers, both Lucky Me and My Legacy are still up for sale.

However, the site is not, as the name implies, a weekly publication - nor is it based in the US capital.

Mr Dougan spent three years as a deputy with the Palm Beach County Sheriff's office, then after he left in 2009 he started a website spreading rumours about his former employers.

Since moving to Russia he has reinvented himself as a journalist covering the invasion of Ukraine, and has spread a number of false and baseless claims - for example that Russia was attempting to destroy biological weapons labs.

Earlier this year Mr Dougan was identified as being a DC Weekly commentator when he gave several talks at an academy affiliated with the Russian Foreign Ministry.

The researchers say the site is part of a much larger pro-Russia propaganda machine.

Mr Dougan said via text message that he "emphatically denies these assertions", and that he sold DC Weekly for $3,000 several years ago.

He said he does not recall the person he sold it to and has lost the paperwork due to being kicked off payment platforms and losing access to email accounts because of financial sanctions against Russia.

He says he has nothing to do with the site's current operations.

"The key point is that it is an important element in a very substantial and effective pro-Russian influence operation that needs to be exposed and understood."

But the attention given to the country's real and ongoing corruption issues has been mild compared to online chatter over false stories backed up by fake documents and shadowy social media accounts.

In October, a widely shared claim on social media stated that President Zelensky's wife spent a fortune on jewellery in New York while the Ukrainian president was in the city speaking to the United Nations.

The video featured a woman who said she is from Benin.

Like the yacht rumour, this claim originated on a YouTube channel with very few followers and just one video.

She claimed to work at Cartier on New York's Fifth Avenue.

The woman showed a receipt dated 22 September, with Mrs Zelensky's name on it and a bill for $1.1m for a bracelet, earrings and a necklace.

Russia's UK embassy X account shared it with the comment: "Best use of UK taxpayers money ever".

But the receipt is a clear fake.

One English-language site was instrumental in spreading the rumour - DC Weekly.