The couple, who rekindled their relationship in July after splitting up after two years together in January, were photographed side by side by a fan at the bash at the Royal Court of Justice after the premiere on Monday night (11.11.13).
The picture, which was posted on Twitter, shows the 23-year-old actress chatting to someone as the British actor, 23, talks on the phone beside her.
Nicholas' sister Rosanna Hoult also attended the premiere.
She tweeted: ''On route to the Hunger Games London premiere. Excited!
''Wonder if we'll have to do a special task to get in, should have brought my bow and arrow in case!''
A source previously revealed that the couple, who remained friends during their time apart, decided to give their romance another chance after spending time together on the set of the movie 'X-Men: Days of Future Past', in Montreal, Canada, which they shot from April until August.
The insider said: ''They started the shoot in April as just friends and then one day they started kissing. One thing led to another and they hooked up. All her old feelings came rushing back. Jennifer has been telling people she's in love again.''
The 23-year-old Oscar-winning actress previously gushed about her love Nicholas.
She said: ''He is honestly my best friend, and hopefully I'm his best friend, too ... I love being around him and he makes me laugh harder than anybody.''
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