Popular young actress and pop star Selena Gomez has revealed the reason behind a recent career break: she was undergoing treatment for the autoimmune disease lupus.

The 23-year-old performer, who grew up in the spotlight thanks to her early success as a Disney Channel star, was forced to cancel several legs of her world tour promoting her debut solo album Stars Dance in 2013 and 2014.

She shared few details at the time and withdrew from public life, which in turn sparked rumours Gomez — who had been dating bad-boy Canadian pop star Justin Bieber — was in rehab.

"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," Gomez told Billboard magazine in a new issue out Thursday.

Selena Gomez (at left) is prepping for a career comeback. She appeared in friend Taylor Swift's hit Bad Blood video. (Jordan Strauss/Invision/AP)

"I wanted so badly to say, 'You guys have no idea. I'm in chemotherapy. You're a–-holes.' I locked myself away until I was confident and comfortable again."

A chronic inflammatory disease, lupus occurs when an individual's immune system attacks its own healthy tissues and organs.

It can affect different body systems, including joints, skin, blood cells the brain, heart and lungs.

Other prominent figures who have lupus include singers Toni Braxton and Seal.

Because of Gomez's celebrity status, she also struggled with public criticism of her physique earlier this year.

"I was in a bikini and got publicly ripped for being overweight," Gomez said.

"That was the first time I'd experienced body shaming like that. I believed some of the words they were saying."

After slowly returning to the public eye — including a prominent role in friend and fellow singer Taylor Swift's hit Bad Blood music video — Gomez is preparing for a career comeback.

She releases her second studio album, Revival, on Friday and — having regained confidence in her body — appears almost completely nude on the album cover.