Is it on between Katie Holmes & co-star Luke Kirby?

Earlier this year, the on-set sparks between Katie Holmes and upcoming film co-star Luke Kirby stirred speculation the two are on the way to becoming a couple.

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Now back on set after a break from filming Mania Days - a Spike Lee film about a romance between a manic depressive poet and a depressed rapper who meet in a psychiatric hospital - the chemistry between the stars is apparently hotting up again, with reports Kirby has recently ended his relationship with his long-term girlfriend, costume designer Andrea Sarubbi.

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Sprung! Katie Holmes and Luke Kirby acting on set during Mania Days filming earlier in the year. Source: getty

"Luke is now a single man, which means that he and Katie are free to explore the feelings that they have to one another," a source reportedly told Grazia magazine in the UK.

Of Holmes and Kirby's communication during the break, a friend reportedly told the magazine that the two 'spoke nearly every day'.

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"It was difficult because he needed to tie up the end of the relationship with Andrea, but there's always been something between them," said the friend.

And the buzz doesn't stop there, with Sarubbi herself reportedly telling the magazine 'things could be going better' in June.

Source: Getty

The pair looked cosy during their first stint of filming in June, and were also spotted having dinner in New York in May this year, according to the Daily Mail.

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Despite their chemistry, a representative for Katie has denied claims of a romance, although an insider thinks there's more than friendship between the co-stars.

"Luke is currently trying to figure out his relationship issues with Andrea. I don't think he knows what to do," an insider told Look magazine.

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"Katie's trying to be a friend to him, as she would to anyone, but the more time they spend together, the more she seems to be falling for him."

Katie Holmes ended her six-year marriage to Tom Cruise mid last year.