The co-stars spoke with ET on Monday at the premiere of their new drama in New York.
On screen and off, Julia Roberts and Ethan Hawke have some genuinely magnetic chemistry -- and they pair can't help but joke around about how well they click.
The pair were all smiles as they walked the red carpet at the premiere of their new drama thriller, Leave the World Behind, at the Paris Theater in New York City on Monday.
While the movie stars spoke with ET's Rachel Smith, the playfully ribbed one another when asked how the pair bonded on set and built their fantastic connection.
"Huge paychecks," Roberts quipped. "And work."
"So much work... it was so much effort," Hawke deadpanned. "It's so hard to get along."
"We're still working on it," Roberts added. "We had someone come and go over some talking points on how to sound like we like each other."
"Yeah, HR came in and helped us out," Hawke joked, as Roberts added, "Yeah they were like, 'This is how you can try to look friendly together.' So we're like, 'OK.'"
According to Hawke, his appreciation for Roberts began long ago when he was shooting the movie White Fang in Alaska, and he felt somewhat lonely and isolated. In an effort to "cheer up the cast" -- meaning him, as the cast was just himself and a wolf -- he watched Roberts' iconic Pretty Woman over and over.
"I watched it many times in Haines, Alaska, and had a great experience," Hawke recalled with a smile.
In Leave the World Behind, Roberts and Hawke play a married couple who are on vacation with their kids at a rental house on Long Island. Their plans are changed when two people (Mahershala Ali and Myha'la) claiming to be the owners show up, and tell them of strange blackouts that have swept the country.
The world begins to fall apart in inexplicable ways as the families struggle to trust each other and figure out how to survive the bizarre and horrifying circumstances.
Leave the World Behind is in theaters now and starts streaming on Netflix beginning Dec. 8.
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