Selena Gomez raised eyebrows when she checked into rehab in January 2014. Despite her rep's insistence that her two-week stint wasn't for substance abuse, those who read the headlines figured that her life had spun out of control, perhaps due to her on-again, off-again relationship with Justin Bieber.

But in an upcoming Billboard cover story, the pop superstar finally spills the reason behind her break: She was diagnosed with lupus.

"That's what my break was really about," she says. "I could've had a stroke. I wanted so badly to say, 'You guys have no idea. I'm in chemotherapy. You're assholes.' I locked myself away until I was confident and comfortable again."

She adds that the constant scrutiny made that process even more difficult: "I'm so fucking nice to everybody, and everyone is so vile to me. I've been working since I was 7. I've been a UNICEF ambassador since I was 17. It's so disappointing that I've become a tabloid story."

Fortunately, Selena channeled her frustration into her new album and debut Interscope release Revival, out tomorrow (October 9). Listen to clips from each song below.