Julia Roberts struggled to be mean to George Clooney while making Ticket to Paradise

Asking Julia Roberts to be mean to George Clooney? Big mistake. Huge.

The actors (and longtime friends) are nearly gleeful as they verbally spar in Ticket to Paradise, out Oct. 21, but when it came time to actually let the other have it, Roberts found it challenging.

In the new film from writer-director Ol Parker (Mamma Mia! Here We Go Again), the iconic actors star as exes David and Georgia, who, despite their mutual loathing, must unite to travel to Bali and try to sabotage the upcoming (and very sudden) wedding of their daughter, Lily (Kaitlyn Dever).

When Clooney and Roberts signed on to the project, Clooney was excited about the opportunity to bring some of the biting wit in the script to life. "George doesn't do romantic comedies, and so he liked the sparring of this," Parker tells EW. "It came from the idea that the opposite of love isn't hatred — it's indifference. If there's still passions there, then there's something to be exploited. And George loved that and went with that."

But things weren't quite so easy for Roberts, particularly when it came to a key scene where Georgia questions whether they are doing the right thing in trying to prevent this marriage from coming off. "The only note I had to give Julia in the whole movie was the scene where they actually argue for real after the marketplace," explains Parker. "They have an argument about how they brought up Lily. Julia was just going easy on George."

"I was like, 'Julia, what's up? What's happening here?'" continues Parker. "George went for it on his close-up and he's still going for it on hers and she's not. I was like, 'What is going on here?'"

"She went, 'I just don't like shouting. I don't like being mean to George,'" explains the director. "And I was like, 'You got to let him have it.' She's like, 'Okay.' And then the next take is the one in the movie. and it's sensational."

Though their characters still hold a lot of lingering resentment over their failed marriage, Clooney and Roberts remain fast friends, always ready to tease each other. But this one scene crossed a line for Roberts emotionally. "She didn't want to be mean to him," concludes Parker. "They like sparring jokingly, but she didn't enjoy doing it for real. But then I gave her note and she killed it. Because she's Julia Roberts."

Related content:

• Inside the lush locations of Julia Roberts and George Clooney's fizzy rom-com Ticket to Paradise
• Julia Roberts says the Clooney family saved her from 'complete loneliness and despair' while filming Ticket to Paradise
• Ticket to Paradise review: Julia Roberts and George Clooney ride a slow boat to midlife romance