The former couple - who split up four months ago after two years together - were spotted ''flirting'' when they met up for an intimate dinner at 'The Little Door' in Los Angeles.
An eyewitness told UsMagazine.com that the 22-year-old Oscar-winning actress and the 23-year-old British actor sat in a private area at the back of the restaurant, sectioned off with curtains.
They were ''happy and laughing'' as they sat across from one another for two hours on what looked to be a ''date''.
The source added: ''They looked flirtatious.''
But a friend close to the 'Silver Linings Playbook' actress suggested their meet up was strictly for professional reasons, as the pair recently began shooting the sequel 'X-Men: Days of Future Past' together.
The insider said: ''They started talking again for the movie's sake. If anything, she broke his heart and they are taking it slow.''
In an interview shortly before their breakup, Jennifer gushed about her love for Nicholas.
She said: ''He is honestly my best friend, and hopefully I'm his best friend, too . . .He's my favourite person to be around and he makes me laugh harder than anybody.''
The 'Jack the Giant Slayer' star continued to voice his support for the blonde beauty after their split was revealed.
After she won the Best Actress Oscar in February, he said: ''I'm very, very happy for her.''