In the crime thriller Dark Places, Charlize Theron plays Libby Day, the sole survivor of a massacre that claimed the lives of her family when she was a young girl, who is still haunted by the violence of her past.

For her role as the troubled and tormented protagonist, Theron sported a cropped ‘do, which she referred to as "the Justin Bieber look."

WATCH: Charlize Theron on Shaving Her Head for Mad Max -- 'I Can't Imagine Doing It Any Other Way'

The Oscar-winning actress spoke with ET on Monday at the Dark Places press junket about why she went that route.

"That was my Mad Max grow out," Charlize explained, referring to her role as Imperator Furiosa in the recent sci-fi epic which required her to shave her head. "I was like, 'We're shooting for 24 days in Shreveport with humidity. I do not think we will be talking about a wig now.'"

So, it was less of a choice and more of a necessity, but it does seem to work for her no-nonsense character.

And it's not just Theron's hair that was influenced by her role in Mad Max. According to the star, she also got her Fury Road co-star Nicholas Hoult to sign on to Dark Places because she wanted the chance to work with him again.

WATCH: Dark Places Trailer Proves It's a Worthy Companion to Gone Girl

"I really wanted to do something with him, and Nick and I always joked on the set of Fury Road that we really didn't get to do much in that film, we were just stuck in the same environment," Theron explained. "So when this came, this was one of the first things I read afterwards, and I immediately thought of him."

Dark Places, based on the novel by Gone Girl author Gillian Flynn, hits theaters Aug. 7.

For more on Charlize's shocking Mad Max: Fury Road transformation, check out the video below to hear the star talk about her wild, post-apocalyptic role.

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