EXCLUSIVE: Jake Lacy Talks 'Dream Come True' Working With Diane Keaton, Teases Sexy 'Girls' Return

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Jake Lacy is ready to help us all get into the holiday spirit.

In his newest film, Love the Coopers, the 30-year-old actor stars as Joe, a soldier who has an accidental meet-up with a beautiful, single girl named Eleanor (Olivia Wilde) at the airport. After the two engage in conversation while waiting for their flights, Eleanor miraculously talks Joe into coming to her extended family's annual Christmas Eve celebration. There's just one catch -- he has to pose as her boyfriend.

WATCH: EXCLUSIVE: Diane Keaton & John Goodman Test the Limits of Sledding in 'Love the Coopers'

The comedy, which opens in theaters today, has a star-studded cast, including Amanda Seyfried, Ed Helms, John Goodman, Alan Arkin and Diane Keaton.

ET caught up with Lacy just ahead of the movie's release, where he revealed behind-the-scenes details from the set, what it was like working with a "dream" cast and an exciting update on his role in Girls.

"The film is incredible," he said. "It's got highs and lows and tears and laughing and this cast is unbelievable. It's Diane Keaton, John Goodman, Ed Helms, Olivia Wilde, who I'm opposite for the majority of the film, so to get to work with those guys, it's an absolute dream come true."

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The cast, he added, became very close, much like how the family bonds together in the holiday film.

"It was freezing cold, it was the coldest winter in Pittsburgh on record," he recalled. "But people were a delight. It was this big family environment. We were all holed together at the same hotel, and we'd eat Saturday night dinner together. There was a real family vibe of everyone coming together. Nothing zany, but just a sweeter, kind place to work. It was amazing."

Watch the full trailer below.

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Lacy also confirmed that he will be returning to season five of HBO's Girls, reprising his role as Fran Parker, Hannah Horvath's (Lena Dunham) coworker turned boyfriend. Last we saw the two, they were bundled up and cuddling together in the snow.

So what's the deal with Hannah and Fran in the new season? Will she keep him around, or rekindle with her ex, Adam Sackler (Adam Driver)? "You get to see over the winter how [Hannah and Fran's] relationship has evolved, and over the course of the season, we see how it continues to spread the sort of layers involved in being in a young relationship," he revealed.

"Yes, things begin complicated," he added, "and they get more complicated."

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Lacy also teased that fans of the show will get to see the two indulge in some heavy romance scenes. "There's a little bit of physical completion of the teased-out relationship that you've seen," he told ET. "There is a fantastic scene in the beginning in which there's some nudity, some physical attention going on. There's also a horrible conversation being had at the same time, which was a delight to do."

To see more from Love the Coopers, watch the video below.