Katie Holmes was spotted giving a steamy kiss to co-star Luke Kirby on the set of her new film Mania Days.

Wearing only a bra, Holmes was making out with Kirby as part of a scripted scene for Mania Days on May 31. Production was filming at an outside location in New York.

Holmes is also rumored to be dating Kirby in real life, making their kiss all the more passionate. Following an outing together in May, New York Post reported that they were very flirty on set and they've been seen "almost holding hands." The pair was also spotted in mid-May enjoying dinner together. When Holmes saw that she was spotted by paparazzi, she allegedly jumped into a nearby taxi, leaving Kirby alone on the street.

See the pictures here.

She may be trying to keep her new boyfriend a secret, as neighbors have described her recent behavior as uncharacteristic. Holmes lives in the Chelsea neighborhood in New York.

"The last month you rarely see her anymore," said one neighbor. "Whatever she's trying to hide I don't know, but she's not going in the main entrance [of her building] any more."

The 34-year-old actress was married to Tom Cruise from 2006-2012. Holmes has primary custody of the pair's six-year-old daughter Suri. Cruise was allegedly upset that Holmes has seemingly moved on to Kirby. One source close to the star said that he'll always love her and he would take her back if he could.

Holmes and Kirby are the two leads in Mania Days, a Spike Lee-produced drama about two manic-depressives who meet and fall in love at a psychiatric hospital. The film is described as a romance that "brings out all of the beauty and horror of their condition."

The film, written and directed by relative newcomer Paul Dalio, also stars Christine Lahti (Chicago Hope). Manic Days is set to be released in 2014.

Watch Holmes and Kirby on the set of Mania Days here:

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