The pair, who were taking part in 60-second cycling competitions on Flywheel bikes in New York City, seemed to be enjoying each other's company as they competed against one another to raise money for Food Bank for NYC.
A source told E! News: ''They were definitely flirting and chatting a quite a bit, although that's not out of character for Jeremy.''
The stars then took their flirtatious chemistry one step further when Nina, who won the cycle challenge, thanked Jeremy on Twitter for taking part in the competition, which was held in Kiehl's since 1851.
She wrote: ''Had so much fun riding for charity @FoodBank4NYC with @Flywheel @Kiehls thanks to @jeremypiven for competing with me. (sic)''.
Jeremy, 48, replied with: ''I want a rematch.''
Meanwhile, the model recently split up with the Wanted's Max George after they began to grow apart.
A source said previously: ''It was hard for Max to dump Nina so soon after news broke that The Wanted are breaking up.
''But they just wanted different things out of the relationship and had grown slightly apart.''
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