The pair - who played lovers in 2006 romantic comedy The Holiday - were apparently caught canoodling at Los Angeles' exclusive Chateau Marmont hotel.
According to an onlooker, Cameron - who has previously dated Justin Timberlake and P Diddy - was openly kissing 39-year-old Jude on the patio before they snuck off to a nearby bungalow.
The source told In Touch magazine: "When someone said, 'Get a room' they listened."
Refusing to read scripts
Mutual friend Gwyneth Paltrow is believed to have tried to set the duo up last year when she took Cameron to watch Jude in Anna Christie at London's Donmar Warehouse theatre and it appears her work has finally paid off.
Meanwhile 39-year-old Cameron is said to be refusing to read for film roles in which the character is over 40 - despite the fact she reaches the milestone in August.
An insider said: "She won't read scripts if the character is 40. Her team asks that the age be changed in the script for Cameron to read for the part."
However, the Hollywood star has previously insisted she doesn't mind getting older.
She told Cosmopolitan magazine: "I think you get better as you age. You know what you want, and you become stronger mentally, emotionally and physically."
24.com publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.
Brody Jenner is ''very proud'' of Bruce Jenner for revealing he is transgender and believes his father has never been happier. Read More »
Amal Clooney wants to complete one of her life goals by appearing on the cover of American Vogue. Read More »
South AfricaHomeMarkR6 000 - R7 000 Per Month
HousesR 1 995 000
HousesR 11 000 000
HousesR 3 990 000