The newspaper said DiCaprio and Tobey Maguire, Fisher's co-stars in "The Great Gatsby," threw a raucous, late-night party to celebrate the film's premiere at the Cannes Film Festival this week.
Married film stars Cohen and Fisher showed up to the party around 3 a.m., dressed for bed and jokingly complained about the noise, the Post said Friday.
"Leo and his pals were partying with a vengeance when Sacha and Isla appeared in robes and slippers, jokingly saying the party was too loud and they couldn't sleep," a source told the newspaper. "Needless to say, the revelry continued and the couple stayed to party. The crowd loved it."