The 'Vampire Diaries' stars, who ended their three-year relationship in May, are reportedly hooking up again but haven't decided whether they will officially get back together.
A source told E! News that Ian, 34, and Nina were all over each other at party to celebrate their show's 100th episode in Los Angeles recently.
A spokesperson for Ian refused to comment.
Nina, 24, ended her short-lived romance with 'Dancing with the Stars' professional dancer Derek Hough last month after just six weeks together.
An insider previously revealed that there was no ''bad blood'' between the brunette beauty and Ian at the time of their split, adding: ''There was no other person involved or any big fight.''
Another source also previously said: ''There was no mean spiritedness behind of either of their motives for ending it.
''The relationship kind of brewed out of a friendship and the fact that they had to get into a romance for the show. The breakup was inevitable.
''I think she decided she wanted to experience other things.''
Paul McCartney is working with Greg Kurstin for his forthcoming new album.
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The critically-acclaimed anthology series may return for a third season, with the first two episodes already written.
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