Selena Gomez just dropped an absolute bombshell about what she's been going through behind-the-scenes before bringing us her Revival. (And no, it doesn't have squat to do with her ex, Justin Bieber.)

Gomez is featured on the cover of Billboard magazine's Oct. 17 edition. In the feature sneak peek, released Wednesday (Oct. 7), she revealed that while gossip blogs would have you believe she was struggling with addiction and who-knows-what else outside of the limelight, she was really undergoing lifesaving chemotherapy treatment.

Yes, really.

Gomez revealed to Billboard that she was diagnosed with lupus -- an autoimmune inflammatory disorder which causes the immune system to attack its own tissues and organs -- and that in order to prevent the disease from becoming potentially fatal, she had to undergo chemo.

"I was diagnosed with lupus, and I’ve been through chemotherapy. That’s what my break was really about. I could've had a stroke," the "Same Old Love" singer explained. "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 also wanted to set the record straight about one thing: Revival does not involve any Bieber Fever.

Gomez had previously given JB some big ups on his upcoming album, but apart from her arguably suggestive "Same Old Love", she insists her ex gets no credit for this album.

"No. This is my time," she said. "I've deserved this. I earned it. This is all me."

Selena's Revival drops Oct. 9.