"A necklace was stolen during the Cannes festival and we are working with the authorities," a De Grisogono spokesman said, refusing to comment on the circumstances of the theft or the exact value of the necklace.
This year's Cannes festival has been plagued by a series of thefts, including the spectacular heist last Friday of a USD 1.4 million worth of jewellery from a hotel room occupied by an American employee of Swiss jewellery-maker Chopard.
France Info radio reported that the missing diamond necklace was worth 1.9 million euros and had been stolen during a gala evening Tuesday at the chic Eden Roc hotel attended by, among others, Paris Hilton and Sharon Stone.
At least two apartments rented by film executives have also been burgled during the festival, with thieves taking cash, jewellery and other personal items.