Prince Rupert Loewenstein, a Bavarian aristocrat and banker who formed an unlikely alliance with the Rolling Stones as their financial adviser, building perhaps the most profitable musical empire in the world, died May 20 in London. He was 80.

His death, from complications of Parkinson’s disease, was widely reported in international news accounts.

Prince Rupert was working in London as a private banker and investment adviser when he was introduced to the Rolling Stones’ lead singer, Mick Jagger, in 1968. The prince, whose interests ran more toward opera and the rituals of the Catholic Church, never did develop a taste for the Stones’ music.

But he did find the band’s financial quandary an interesting challenge. For all their chart-topping success in the late 1960s, the Stones were locked into unfavorable contracts that saw most of their earnings scooped up by record companies and unscrupulous managers.

For the first three years that he advised the band, Prince Rupert accepted no fees. He soon gained the confidence of Jagger, who had attended the London School of Economics, and the other band members.

Over time, he launched the band on hugely successful worldwide tours and guided the group toward heights of prosperity and decades-long success seldom seen in popular music. He was also, with his bald pate, Savile Row suits and aristocratic bloodlines, the most anomalous member of the Stones’ inner circle.

“To many outsiders it must seem extraordinary that I was never a fan of the Stones’ music, or indeed of rock ’n’ roll in general,” Prince Rupert wrote in his 2013 memoir, “A Prince Among Stones.” “Yet I feel that precisely because I was not a fan, desperate to hang out in the studios . . . I was able to view the band and what they produced calmly, dispassionately, maybe even clinically — though never without affection.”

By 1972, Prince Rupert had extricated the band from an onerous arrangement with an American adviser, Allen Klein, but the legal wrangling continued for decades.

Prince Rupert also suggested that the Stones move their primary residences out of the United Kingdom, where taxes claimed as much as 98 percent of their profits. He recommended the South of France, where the Stones completed one of their most celebrated albums, “Exile on Main Street,” in 1972.

The record “may be one of the few top-selling albums,” Prince Rupert wryly noted, “to contain a reference to financial planning in the title.”

When the prince came on the scene, he was appalled to learn of the haphazard accounting practices commonplace at even the loftiest levels of rock-and-roll. Even in the 1970s, it wasn’t uncommon for promoters to pay the band with paper bags stuffed with cash.

Prince Rupert abolished that practice and restricted the number of free tickets distributed to concerts. He professionalized the band’s entourage, with clear work assignments, and was ruthless against scalpers and scheming promoters.

He also saw the importance of merchandising and brand recognition and, among other things, obtained a copyright for the Rolling Stones’ logo of a tongue extended from bright red lips. He sought out lucrative sponsorships from major corporations and licensed the band’s music for commercial use.

In just one instance, the Stones made millions by allowing Microsoft Windows to use the opening phrase of “Start Me Up.”

Prince Rupert’s services to the Stones extended to legal matters as well, including Jagger’s divorce from Bianca Jagger and Keith Richards’s 1977 arrest in Canada for trafficking in heroin.

He conceived a novel strategy for Richards to reduce the charges to simple possession by showing that the guitarist made so much money from music that he didn’t need to sell drugs.

“Our defense,” the prince wrote in his memoir, “was that rich people tend to buy ten packets of cereal for their kitchen cupboard in one go, but you would never say that they were dealing in cereal. This was the same thing: a rich man had bought a lot of heroin for his personal use because he thought the price was good.”

From then on, Prince Rupert advised the Stones not to carry drugs across international borders.

With his vast social connections, the prince was known to throw lavish parties that featured members of the Stones mingling with Hollywood stars and royalty. After one noisy all-night party at his house, neighbors called the police to restore order, only to be told, “We can’t do anything about it. Princess Margaret’s there.”

Prince Rupert was born Aug. 24, 1933, on the Spanish island of Majorca. His heritage was Bavarian, and members of his family had been part of the European and South American nobility for centuries. His full name was Prince Rupert Louis Ferdinand Frederick Constantine Lofredo Leopold Herbert Maximilian Hubert John Jenry du Loewenstein-Wertheim-Freudenberg, Count of Loewenstein-Scharffeneck.

He lived in England from the age of 6, primarily with his divorced mother, who sometimes sold family heirlooms to buy food.

He graduated from Magdalen College at the University of Oxford, then became a stockbroker and financial adviser in London. He and two business partners bought the banking firm of Leopold Joseph & Co. in 1962 and advised wealthy clients.

Survivors include his wife of 56 years, Josephine Lowry-Corry; and three children.

Prince Rupert was a devoted Catholic, and one of two sons entered the priesthood; the other became a monk.

The prince retired from advising the Rolling Stones in 2007, after he suggested that it might be time for the aging rockers to settle into a comfy retirement. When he published his memoirs last year, he received unexpected criticism from Jagger, who is now worth hundreds of millions of dollars, thanks to the prince.

“Call me old-fashioned,” Jagger said, “but I don’t think your ex-bank manager should be discussing your financial dealings and personal information in public.”

Prince Rupert wrote in his book that he “never played a Stones track by choice. I did find some Rolling Stones songs moving. . . . But by and large it was rather like the circus. When one stops being a child, the circus becomes a bit of a bore.”