Two mystery Leonardo fans each bid $1.9 million to secure a pair of seats on the Virgin Galactic's space flight
Earlier this week it was reported that the actor had put his name to one of the biggest prizes at the amfAR gala in Cannes.
Up for grabs was the chance to take a trip on Virgin Galactic's space flight accompanied by Leonardo.
The auction took place at the Hotel du Cap in France last night and the space trip raised almost $4 million for charity.
Places on the world's first commercial space trip usually cost around $200,000, however this journey was described as "priceless" since the passenger will have the pleasure of Leonardo's company as they leave Earth behind.
Virgin boss Richard Branson is hoping to start launching flights at the end of the year.
The space trip wasn’t the only prize involving Leonardo that attracted a great deal of interest. Also on offer was the chance to attend the premiere of the 38-year-old’s new movie The Wolf of Wall Street with him. That went for an impressive $1.5 million.
Guests also splashed out on prizes that gave them admission to one of the glitziest Oscar parties next year.
Organisers decided not to reveal the names of the lucky bidders raising money for the amfAR Cinema Against AIDS event.
The gala, hosted by Sharon, also welcomed Jessica Chastain, Janet Jackson, Milla Jovovich and Goldie Hawn, with performances by Duran Duran and Shirley Bassey, who sang Goldfinger.
Luxury prizes up for auction included an Andy Warhol lithograph of Elizabeth Taylor, a chance to have a family portrait taken by photographer Annie Leibovitz, a week in fashion designer Donna Karan's Caribbean hideaway and a shimmering 53-carat diamond necklace.
Annie said: "Yes, you can think it's a silly little dinner, you can deride it as full of celebrities dressed up. But that's missing the point. Eighty million dollars amfAR has raised since it began. That's the point. It has saved lives."
Movie mogul Harvey Weinstein told the crowd that while two decades ago the illness was a "looming plague," a cure might well be seen within "our lifetime".
amfAR put on a catwalk show at the gala for the second year, featuring 38 gold and black looks from designers such as Dior, Chanel, Lanvin and Prada, worn by models including Karlie Kloss, Karolina Kurkova, Angela Lindvall and Alessandra Ambrosio.
Guests were wowed by a custom gold embroidered long-sleeved gown from Valentino, and a custom gold pleated minidress from Givenchy. All the dresses went to a single bidder, selling in just a couple of minutes for 1.56 million dollars.
This year's Cannes has seen two jewellery heists so far, one of which was the theft of a two million euro necklace.
Actress Milla said: "I'm going to be watching how much champagne I drink, because you never know, somebody might come up and just shwoop, take it off."