Actress Charlize Theron is no stranger to physically transforming herself for a movie role — but, to her surprise, gaining weight for her latest film led to a mental health battle. During a new interview, the 42-year-old Oscar winner revealed that she suffered from depression after gaining 50 pounds to play a modern mom-of-three in Tully.

"I gained close to 50 pounds for this film. I just I wanted to feel what this woman felt, and I think that was a way for me to get closer to her and get into that mindset. You know, it was a huge surprise to me. I got hit in the face pretty hard with depression. Yeah, for the first time in my life I was eating so much processed foods and I drank way too much sugar. I was not that fun to be around on this film," Charlize recently told Entertainment Tonight.

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Charlize in Tully.

The actress explained that she had about three months to gain weight to portray an overworked and exhausted mother who is gifted a nanny in Tully. "The first three weeks are always fun because you're just like a kid in a candy store. So it was fun to go and have breakfast at In-N-Out and have two milkshakes. And then after three weeks, it's not fun anymore. Like, all of a sudden you're just done eating that amount and then it becomes a job. I remember having to set my alarm in the middle of the night in order to just maintain [the weight]," she shared.

"I would literally wake up at two in the morning and I'd have a cup of cold macaroni and cheese just next to me," Charlize continued. "I would wake up and I would just eat it… I would just, like, shove it in my throat. It's hard to maintain that weight."

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Charlize in Tully.

Funnily enough, Charlize's own two children — six-year-old son Jackson and two-year-old daughter August — thought their mom might be having a baby when they noticed her weight gain. "My little one was convinced that I had a baby in my belly. I had a very similar moment with my older one. Like in the film, where she saw my body one day and was like, 'Mom, what has happened to your body.' It was a little too close to home. I shared it with [director Jason Reitman] and I was like, 'This is a little too real for me.' And [my kids] still refer to this movie as the movie where mommy had a big belly," she said.

After she wrapped shooting on Tully, Charlize said it took her more than a year to lose the weight she had put on. "There's nothing fun about that. It took about a year and a half. It was a long journey, very long journey. And it's hard because I had press junkets and movies around it and nobody knew that I had done it for this. And I think in the beginning everybody thought I was wearing, like, when the first photos came out, everyone [thought it] was, like, prosthetics. And then I went on press junkets and it was like nobody knew," she recalled.

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Charlize in Monster.

This interestingly isn't the first time Charlize has gained a significant amount of weight for a movie. Back in the early 2000s, she put on 30 pounds to portray serial killer Aileen Wuornos in Monster. This time around, she admitted it was much harder to lose the weight because she is now older. "I was worried. I was like, this is taking a really long time. Because on Monster, I just didn't snack for five days and I was fine. You know your body at 27 is a little different than your body at 43, and my doctor made sure to make me very aware of that. Like, you are 42, calm down, you're not dying, all good," Charlize shared.