Among the 900 guests mingling at a star-studded charity event hosted by Leonardo DiCaprio in St-Tropez last week was – perhaps predictably – a Swiss private banker: Julius Baer CEO Boris Collardi. Why?

The event, dubbed «the most amazing celebrity auction of all time» by influential U.S. business magazine Forbes, drew more A-listers than some award shows.

Guests included Cate Blanchett, U2’s Bono, George Clooney,Reese Witherspoon, Steven Spielberg, Robert DeNiro, Chris Rock and Bradley Cooper.

A slew of supermodels seemed to follow Leonardo DiCaprio just about everywhere, also attended.

DiCaprio's Rolex, Scorcese Film Experience

Guests bid on items such as DiCaprio’s Rolex, a private dinner at the Eiffel Tower closed off to tourists, a week on the set of Martin Scorcese’s new film, a private theater performance by Kevin Spacey at home, a tour of Monaco with Prince Albert, a training day with Premier League team Manchester United, and artworks by Pablo Picasso, Jeff Koons and Damien Hirst.

Baer has sponsored the event three years running, but doesn't disclose what the association costs. This year, DiCaprio raised $45 million for personal charity, with the help of prominent Swiss auctioneer and art collector Simon de Pury, who conducted the live auction.

Part of the Job

The charity auction has prominent «chairs,» or a sort of board set up to oversee the evening. Its members are Blanchett, De Niro, Marion Cotillard, Philippe Cousteau Jr., Penelope Cruz, Jonah Hill, Kate Hudson, Scarlett Johansson, Tobey Maguire, Edward Norton, Arnold Schwarzenegger, Kevin Spacey, Charlize Theron, Chopard co-president Caroline Scheufele – and Collardi.

To be sure, hobnobbing with the rich is pretty much a core part of every private banker’s job. Sponsoring is also a crucial part of private banks’ offerings – they are a savvy way to offer an immaterial good or an experience to wealthy clients who already have everything, while dispersing the bank's brand in a favorable way.

Baer in Limelight

Performers at the St-Tropez event, which included Mariah Carey and Lana del Rey this year, appeared against a blue backdrop emblazoned with the logo of DiCaprio’s Foundation, as well as Julius Baer's.

This represents a far higher profile engagement than Baer’s other sponsoring activities, which the bank also isn’t required to provide any financial or other disclosure on.

Those include supporting the British Museum, sponsoring a polo tournament in the «German Hamptons,» or Sylt, and the Zurich Opera.

Undisclosed Sum

Baer also operates its own charitable foundation which supports youth projects around themes such as preventing violence, health and sports, and vocational training. This engagement, a vestige of when Baer was a family-controlled and -operated bank, is typically done behind the scenes and with little public fanfare.

The bank gifts DiCaprio’s foundation, LDF, an undisclosed amount to appear as a sponsor of the St-Tropez auction as well as for Collardi to act as an event chair.

LDF, which is devoted to environmental causes, isn’t required to disclose any financials because of its status as a foundation, but it says it has granted $30 million in the last six years to 76 projects – from protecting Indonesian coral reefs to wild tigers in Nepal.

Feeder Fund

DiCaprio’s entity makes use of a system of community foundations that are commonplace in the United States: LDF is a component fund of the California Community Foundation.

This means DiCaprio’s foundation doesn’t pay taxes or have to provide the same type of accountability that private foundations do. The structure is perfectly legal, if controversial in charitable circles for its lack of transparency.

DiCaprio's credibility as an environmentalist has taken a beating after he was mocked in climate circles for frequently using eco-unfriendly private jet travel between Europe and the U.S.

60 Prospective, Current Clients

Collardi, who has given the event his backing for the third year in a row, clearly relishes the event's glamour – which certainly provides a change of scenery from his day job.

«Because this is a client event with a select group of international clientele, the presence of our CEO makes sense and fits the occasion,» a spokeswoman for Baer said.

The bank sent Collardi and Europe head Remy Bersier to the event, to which it invited 60 current and prospective clients – and had several of its private bankers in attendance.

Formula E Link

DiCaprio and the bank have another, less high-profile link. The actor co-founded the Venturi team three years ago, which competes on the Formula E circuit. Julius Baer is the global sponsor for Formula E, the first fully-electric racing series.

DiCaprio chairs the circuit's Sustainability Committee, which Collardi also sits on.

Baer's engagement in Formula E racing isn't related to DiCaprio's involvement, which predates the bank's, according to a source.