Afterward Rybolovlev would retire to his penthouse, the Belle Époque, with its kingly view of Port Hercules and the ancient palace, where he attended the christening reception for the prince’s twins in 2015.

Lately though, Rybolovlev, a billionaire Russian mining magnate, has been less visible, and Prince Albert has maintained a delicate, diplomatic distance from him.

Rybolovlev is still a force here, of course, owing primarily to his soccer team, whose success drew a recent grateful acknowledgment from the prince.

But for the past year, a local magistrate has been reviewing whether Rybolovlev used lavish perks and soccer passes to enlist Monaco law enforcement officials as allies in his long-running feud with a Swiss businessman, Yves Bouvier.

It’s a quarrel that began several years ago when Bouvier helped Rybolovlev buy 38 pieces of world-class art for a startling $2 billion. Rybolovlev has said in court papers that he believed Bouvier was acting as his agent and adviser on the transactions, and he earned fees for that service. But he later found, he said, that Bouvier had bought many of the items in advance, then flipped them to him at a markup of $1 billion.

In 2015, Monaco officials arrested Bouvier on fraud charges related to Rybolovlev’s complaint. The magistrate is investigating whether that decision was unduly influenced by Rybolovlev’s generosity, a premise his representatives have vehemently denied.

“Monaco Football Club is only continuing the practice of invitations established before the purchase of the club by Rybolovlev,” said Brian Cattell, his spokesman, “and corresponding to the practice of most major clubs in France. It is absolutely legal.”

The dispute is far from the only reason Rybolovlev’s profile has risen so drastically. His purchase of Donald Trump’s Palm Beach mansion for $95 million in 2008 has made him a mainstay in recent speculation about Trump’s Russian “connections.” And his sale of Leonardo da Vinci’s “Salvator Mundi” for $450 million, the most ever paid at auction for a painting, instantly elevated his art market profile.

But in Monaco, where Rybolovlev’s flourishing soccer team has made him a celebrity, he is also known for his role in what Prince Albert refers to as “the Rybolovlev Affair.”

Bouvier has said that, like any art dealer, he was entitled to charge Rybolovlev whatever he wished. His case has yet to be adjudicated, and Bouvier, who was released soon after his arrest, continues to live in Switzerland.

The review of Rybolovlev’s conduct in the matter began with the disclosure that his Swiss lawyer, Tetiana Bersheda, had exchanged multiple text messages with Monaco’s top police and justice officials.

Bouvier’s side says the messages show Bersheda alerted the Monaco police about Bouvier’s arrival there for a business meeting, at which he was arrested.

Monaco’s justice minister, Philippe Narmino, resigned last year when his texts to Bersheda became known. One included a grateful acknowledgment from his wife for a 2015 helicopter trip to Rybolovlev’s Swiss chalet for skiing and a dinner hosted by a diamond merchant.

For months, the magistrate exploring the accusations of undue influence by Rybolovlev has been questioning the principality’s elite and exploring bank accounts. In recent weeks the French media revealed how Rybolovlev’s team had courted the local authorities with perks and tickets. Prince Albert has vowed that no misconduct would be tolerated and also suggested the reports and leaks about the investigation threaten to damage Monaco’s institutions.

“It’s a story that has all the qualities of a dark detective novel,” said Renaud Revel, author of “The Mysterious Rybolovlev.”

“It’s a portrait of a king,” he said, “without a crown, who turned the rock of Monaco into an opaque system of favors.”

Outside Monaco, Rybolovlev’s name routinely surfaces in articles about Trump’s Russian ties. The two men say they have never met. But their real estate deal, in which a Rybolovlev family trust bought Trump’s estate, has drawn the interest of one U.S. senator, Ron Wyden, D-Ore., who asked the Treasury Department for any records it might have on the transaction.

The price paid for the 6-acre property was a surprising markup from the $41 million Trump had paid only four years earlier. But Rybolovlev is on the way to recapturing the sum after having subdivided the property. Two of the three parcels have together reaped a total of $71 million.

Rybolovlev also did well with his Leonardo painting. As a matter of public relations, the profits generated by that $450 million sale have undercut the view of Rybolovlev as victim, since he only paid Bouvier $127.5 million for the work in 2013. (Bouvier had paid $80 million for it.)

But Rybolovlev has continued to pursue civil complaints against Bouvier in several places, as part of an effort to demonstrate that the Swiss businessman defrauded him by not acknowledging that he often acted as an independent middleman, not a fee-based adviser.

“The record sale of the painting of Leonardo da Vinci was a great success, but it changes nothing in relation to the hidden profit made by Bouvier,” Bersheda said. “My clients are entitled to the difference between the misrepresented price and the real price.”

In Monaco, Bersheda functioned as Rybolovlev’s ambassador to the local elite and prominent charities, leading the Friends of the Ballet de Monte-Carlo. Russian expatriates are increasingly visible in this microstate of millionaires where there is no income tax and where luxury stores employ Russian-speaking employees.

But late in 2016 she moved her orbit from Monaco to London, where she continues to represent Rybolovlev, and has created a boutique law firm. She remains president of the ballet and a board member of the soccer team.

As part of the influence peddling investigation, searches were conducted last year of the home of Narmino, the justice minister, and the Monaco Red Cross, where he remains a vice president.

The investigation is also reviewing whether the soccer team used its popularity to become chummy with the Monaco authorities. A former Monaco policeman has told the investigators that as many as 25 law enforcement officials obtained pairs of free VIP season passes valued at about $16,000 a pair, according to a transcript of his account. Rybolovlev’s representatives say courtesy passes are an established practice in the league.

The investigation grew out of an invasion of privacy complaint lodged against Rybolovlev and Bersheda in 2015 by Tania Rappo, a resident of Monaco who was once a close friend of Rybolovlev. Rappo accused Bersheda of illegally recording their personal conversation at Rybolovlev’s Monte Carlo penthouse in 2015.

Bersheda insists she was only aiding the Bouvier investigation because Rappo had assisted on some of the disputed art sales. Bersheda turned over her phone to the Monaco authorities to confirm that the conversation had not been edited. She objects to the fact that the police then also scrutinized her erased text messages.

“It is shocking that the same authorities subsequently used my phone for unrelated purposes, flagrantly breaching procedural rules, my own privacy and the legal privilege I enjoy as a lawyer,” she said.

Rybolovlev has challenged the scrutiny of his lawyer’s private telephone, but the court rulings have gone against him.

Bouvier’s lawyer in Monaco, Frank Michel, said some people would like the influence-peddling investigation to end.

“I don’t know how powerful Rybolovlev is now,” he said. “This is precisely the reason for the investigation. There are many elements that lead us to believe there is a system of corruption, not only with one official, but a general system.”

Rybolovlev’s jet-setting absences from Monaco have fueled speculation that he plans to decamp and preside over a team in another country — perhaps Italy. His representatives deny the reports. Rybolovlev declared his fealty in an interview with a French television channel this summer, “I love this club and the principality.”

Sergei Chernitsyn, an adviser to Rybolovlev, has said repeatedly that Rybolovlev is satisfied with his Monaco penthouse, purchased for a reported 300 million euros and renovated this year.

“He is happy,” Chernitsyn said, adding in regard to the penthouse, “As always in business, if somebody comes and proposes — let us say 1 billion euros — in theory it could be discussed.”

This article originally appeared in The New York Times.

Doreen Carvajal © 2018 The New York Times