It was an intimate gathering.

A select group of Russian businessmen assembled for a black-tie dinner at Dumfries House, the stately home restored for the nation thanks to a major fundraising campaign by the Prince of Wales. The heir to the throne wanted to thank his donors in person.

One of them was Ruben Vardanyan.

A well-known philanthropist, he ran an investment bank, Troika Dialog, an independent arm of which moved vast amounts of private wealth out of Russia into Europe.

Troika is under the spotlight because staff from this independent division administered a network of shell companies that appear to have mixed legitimate and illegitimate money.

Vardanyan didn’t know anything about this. Neither did Prince Charles. There is no criticism of either of them.

But leaked banking records underline once again the problems created by opaque transactions that allow vast amounts of money to flow from Russia into the western banking system.

The relationship between the prince and the financier began in November 2009, when Vardanyan made a charitable donation of $100,000 to the Prince’s Charities Foundation – then a key fundraising vehicle for Charles’s charitable work.

The payment came not from Vardanyan’s personal account, but was transferred from an account at Ukio Bank in Lithuania belonging to a shell company registered in the British Virgin Islands – Quantus Division Ltd.

Via Lithuania, Quantus moved over $700m into the global banking system from its creation in 2006 until Ukio was declared insolvent and closed down by the authorities in 2013.

Two more payments to the foundation followed, from the same source. Quantus sent £38,000 in January 2010 and £25,000 in May 2011, with records showing the last donation was received at a branch of Coutts in the Strand, London.

In total, the foundation received $200,000.

Vardanyan says the payments were in support of a programme to “preserve architectural heritage in England”.

Explaining why they came from Quantus, he said: “I instructed my office to transfer funds to the Prince of Wales charity fund. I did not go into detail about which financial and settlement centre the transfer would be made through, but my office was in charge of these details.”

The prince’s foundation had been left with a big financial hole to plug. The cause? A £20m loan it had taken out to buy Dumfries House.

In 2007, after hearing it was to be sold to a private buyer, Charles stepped in. He raised £45m for the stately home, which contains a unique collection of Chippendale furniture. His intervention came not a moment too soon. Lorries were already carrying the antiques to the auction house. One day, at 1am, they were stopped on a Cumbria motorway and turned back.

The battle to rescue Dumfries did not end there. Soon, there were questions over whether the loan could be repaid.

In a documentary about the rescue, the prince told ITV: “You know you wake up in the middle of the night thinking, help … having done the actual deal, then a year later or two years later the bottom fell out of the market, didn’t it? … overnight, the value of everything went right down.”

Charles redoubled his fundraising efforts. In February 2010, he hosted Armenian dignitaries at a dinner at Windsor Castle. In 2013, Armenia hosted Charles on a private visit.

The networking paid off.

Through his UK registered charity, Vardanyan raised a further £1.5m to refurbish The Mains, one of the estate’s outbuildings, providing 16 luxury rooms that could be rented out to visitors. The money came from his own pocket, and those of other Russian donors – though not from the Troika Laundromat.

By then, Troika had been sold, with Vardanyan taking his share of the reported $1bn price.

In return for his generosity, the structure has been renamed The Dilijan Building, after a school in Armenia sponsored by Vardanyan. A 10-year partnership was created, with students from Dilijan attending regular courses at the estate.

Vardanyan’s website lists the Dumfries donors. Their photos are there too, shaking hands with the prince, presenting him with a gift, and later in tuxedos and evening gowns for the formal dinner Charles hosted in 2014 to mark the completion of the project.

It is understood Troika Dialog had never been fined by any regulatory body or law enforcement agency and had at all times observed international standards of transparency and compliance.

Vardanyan was never involved in the operations, management or activities of the independent arm of the bank that administered Quantus and other offshore companies. This division was, he said, created to help manage family money for private clients.

He did have an account and his own funds at the division, and it is understood he paid fees for the service set at a commercial rate.

“The Prince of Wales’s charities operate independently of the prince himself in relation to all decisions around fundraising,” a Clarence House spokesman said.

In a statement, the prince’s charities said they apply “robust due diligence processes” in accordance with Charity Commission and Scottish Charity Regulator guidelines and money laundering legislation. They said the donations in question had raised no “red flags” when checks were being made.

It was not unusual for donations to be sent through offshore accounts, the charities stated, adding that they would not rule out such payments in future – provided they adhere to all relevant guidelines.

Additional reporting by James Oliver.