Demi Lovato Says She Was Raped at 15 During Disney Days

Demi Lovato says she was sexually assaulted as a teenager and is opening up about it for the first time, publicly ... because it's taken her this long to process the trauma.

The singer made the shocking revelation in her new documentary, 'Dancing with the Devil' ... which premiered Tuesday night at SXSW. In the film, she says, "I lost my virginity in a rape."

The film infers the alleged assault occurred when she was 15 during her days as the Disney Channel star of "Camp Rock" and "Sonny With a Chance." Demi says she called the person back a month after the alleged rape and "tried to make it right by being in control and all it did was make me feel worse."

She says of the encounter ... "We were hooking up but I said -- hey, this is not going any farther, I’m a virgin, and I don’t want to lose it this way. And that didn’t matter to them, they did it anyways. And I internalized it and I told myself it was my fault because I still went in the room with him. I still hooked up with him."

Demi claims she developed a serious eating disorder to deal with the trauma, and beat herself up for years ... but she feels it's finally time to share her truth.

As we reported ... the new documentary details Demi's 2018 overdose -- including being declared legally blind in the hospital after she woke up -- along with her many other challenges and triumphs.