Demi Lovato: "I Was Bullied Because I Was Fat"

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Demi Lovato continues to open up about the "emotional issues" that landed her in rehab last November.

VIDEO: Demi opens up about the "darkest time" of her life

In an interview with ABC's Robin Roberts, the 18-year-old singer-actress said childhood bullying contributed to her eating disorder.

"I literally didn't know why they were being so mean to me," she said of her childhood tormentors. "And when I would ask them why, they would just say, 'Well, you're fat.' I was bullied because I was fat. And then a few months later I developed an eating disorder, and that's kind of what I've been dealing with every since."

Lovato was "compulsively overeating when [she] was 8 years old," and said for the past 10 years, she's "had a really unhealthy relationship with food."

The star addressed one of her lowest points: when she physically struck Alex Welch, one of her backup dancers, in November 2010. (After the incident, Lovato pulled out of the Camp Rock 2 Tour with the Jonas Brothers and checked into rehab.)

"I take 100 percent full responsibility for that. I feel horrible. [She] was my friend," she said. Lovato's behavior caused her family and management team to hold an intervention. "They sat me down and said, 'You can't live like this.' And the only way that you're going to get the help that you need is to go in-patient to a treatment center. And that's exactly what I did."

Photo credit: Jordan Strauss Wireimage.com