Benefit officials said the Fringe star, 33, accompanied by his longtime love, Diane Kruger, won a necklace by designer Carla Amorim with a bid of $45,000. The "Boreal" necklace is made with 11.7 carats of white diamonds set in 18k rose gold.
Jackson was reportedly overheard saying it was an engagement present for her. Sources close to the couple, however, say engagement buzz is not true.
Jackson and Kruger, 35, who wore a cream-colored Prabal dress, and Rose McGowan, wearing Monique Lhuillier, were among the celebrities who drove in from the Cannes Film Festival for the dinner at the Hotel de Paris.
Prince Albert hosted the gala with his sister Princess Caroline and Albert's cousin Baroness Elizabeth-Anne de Massy, and President Clinton gave a brief speech.
Guests dined on farm-raised veal, fish, zucchini caviar and truffled vinaigrette from Hotel de Paris master chef Alain Ducasse.
Albert's wife, Princess Charlene, was not present. Palace officials said the dinner was meant to be a "gentlemen's evening" and that the 34-year-old princess did not want to "take away" from Albert and Clinton's announcement that their foundations will work together on global issues such as environment, health issues and more.
Courtesy Carla Amorim