This post deals with abuse and might be triggering for some readers.

For more than two decades, we've seen Paris Hilton's life play out in front of cameras, but there's been one thing she has kept private the whole time.

As a teenager, she was allegedly mentally and physically abused at a boarding school.

Hilton, 40, has been in the public eye for much of her life; first as a socialite then a TV star, model, singer, actress and DJ. But mostly, Hilton is known for being one of the first celebrities to become 'famous for being famous'.

Last year, Hilton let viewers inside her life as part of a YouTube documentary This Is Paris.

WATCH: The 'ThisIs Paris' trailer. Post continues below video.

In the documentary, which was released in September, Hilton explained that she felt like "the whole world thinks they know me," but often she doesn't even feel like she knows herself.

She also spoke about her childhood trauma for the first time publicly.

"Something happened in my childhood that I've never talked about with anyone," she said.

"But I couldn't tell you guys, because every time I tried, I would get punished by them," she continued. "I still have nightmares about it. The only thing that saved my sanity was thinking about who I wanted to become when I got out of there. I just created this brand and this persona and this character, and I've been stuck with her ever since."

In an interview with People, Hilton said she "buried her truth for so long".

She was sent to Utah's Provo Canyon School in the late 1990s, after her parents became sick of her disobedience, that saw her sneak out to go to clubs and parties.

"I knew it was going to be worse than anywhere else," Hilton said.

"It was supposed to be a school, but [classes] were not the focus at all. From the moment I woke up until I went to bed, it was all day screaming in my face, yelling at me, continuous torture."

Hilton said she thinks the staff's goal was to "break" the students.

"They were constantly making me feel bad about myself and bully me. I think it was their goal to break us down.

"And they were physically abusive, hitting and strangling us. They wanted to instil fear in the kids so we'd be too scared to disobey them."

Hilton said she had daily panic attacks and cried each day she was at the institution, which would put students into solitary confinement for up to "20 hours a day" if staff discovered any plans to escape.

"I was just so miserable. I felt like a prisoner and I hated life," Hilton toldPeople.

She has also shared that if it wasn't for the abuse in school, she wouldn't have met her ex-boyfriend and made her leaked sex tape,1 Night in Paris.

"I would never have let anyone into my life like [the man in the tape, whom she was dating at the time]. I met the worst person I could meet and if I hadn't gone to Provo, I wouldn't have entertained the thought of letting him into my life. Provo affected my future relationships," she told People in her latest interview.

Hilton shared that after experiencing such trauma, she didn't understand the difference between love and a relationship.

"I thought that them getting so crazy meant that they were in love with me. Looking back, I can't believe I let people treat me like that," Hilton said.

"I went through multiple abusive relationships. I was strangled, I was hit, I was grabbed aggressively. I put up with things no one should.

"They all seemed like such nice guys and then the true colours would show. They'd get jealous, or defensive or try to control me. And there would come a point where they would become physically, verbally and emotionally abusive."

In her documentary, Hilton said "I'm so used to like, playing a character that it's hard for me be normal".

"Everything I’ve ever done before was more of me just playing that character again. But with this I really just wanted to pull the curtain back and show my real life and talk about things that were very hard to talk about and things that I've experienced in life that I’ve never talked about before."

An heiress and socialite turned TV star.

Hilton, the oldest of four children, was born into American business royalty. Her paternal great-grandfather was Conrad Hilton, the founder of Hilton Hotels.

Her childhood was mostly split between Los Angeles and New York City, and her friendship group consisted of other wealthy children of famous people, including Ivanka Trump, Kim Kardashian and Nicole Richie.

When she was a teenager, she spent a year at the Utah school for 'emotionally troubled teens'.

"It's time these places go down and get what they deserve," Hilton wrote on the Instagram account of Breaking Code Silence, "a movement organised by a network of survivors and activists to raise awareness of the abuses in the Troubled Teen Industry".

In the documentary, three of Hilton's former classmates will back up her accusations of abuse, including claims they were force-fed medication and held down by restraints as a form of punishment.

She toldPeopleshe didn't often speak to her family during her time in Utah, only being able to call once every two or three months.

"We were cut off from the outside world. And when I tried to tell them once, I got in so much trouble I was scared to say it again. They would grab the phone or rip up letters I wrote telling me, 'No one is going to believe you.' And the staff would tell the parents that the kids were lying. So my parents had no idea what was going on."

Hilton left the school after 11 months, but refused to speak about her experience.

"I was so gratefu