Cat burglars struck Cannes again in the film festival’s biggest heist yet, snatching a $2.6 million diamond necklace. It was stolen following de Grisogono’s bash Tuesday at the Hotel du Cap Eden-Roc where 700 guests, including Sharon Stone, circulated. The piece was displayed as part of the line’s launch of its 20th anniversary High Jewelry Collection. “With over 80 guards and additional police on the grounds, the necklace went missing,” said a source. “Fawaz Gruosi has done this party at the du Cap for 12 years, and nothing like this ever happened.” Company founder Gruosi released a statement saying an investigation has been launched by local police, adding, “These incidents are rare . . . However, when they occur one must be proactive and collaborate with the authorities.” Cannes has been marred this year by robberies, including $1 million worth of Chopard jewels stolen from a safe, hotel rooms cleaned out and a reported mugging. China Film Group exec Zhang Qiang posted, “Security in France is so bad” after all his luggage was stolen.