The 23-year-old singer told Billboard she was forced to put her career on hold when the diagnosis was made.

"I was diagnosed with lupus, and I've been through chemotherapy," she told the publication.

"That's what my break was really about. I could've had a stroke."

Lupus is an autoimmune condition which causes painful body tissue inflammation.

The condition normally results in joint pain and swelling, but can also cause sensitivity to light, skin rashes and hair loss.

Gomez recently took an (until now) mysterious break from the spotlight.

In December 2013, Gomez cancelled the Australian and Asian legs of her Stars Dance world tour, stating that she needed some "me" time.

"My fans are so important to me and I would never want to disappoint them," Gomez said in a statement released at the time.

"But it has become clear to me and those close to me that after many years of putting my work first, I need to spend some time on myself in order to be the best person I can be."

Two months later, Gomez's representatives confirmed to People that the singer had spent two weeks in an Arizona rehabilitation facility, although they said her stay was "not for substance abuse".

During her absence, tabloid speculation was rife that Gomez had been greatly affected by her breakup with singer Justin Bieber, whom she dated from 2011 to 2014.

There were also rumours Gomez was suffering from a drug addiction, like other child stars before her.

"I wanted so badly to say, 'You guys have no idea. I'm in chemotherapy. You're assholes,'" she told Billboard.

"I locked myself away until I was confident and comfortable again."

Gomez returned to her singing career late last year with her song The Heart Wants What It Wants.

The singer/actress, who found fame as a child on the Disney Channel's Wizards of Waverly Place, has recently been doing press for her new album, Revival, and has opened up about her life as one half of a teen celebrity couple.

Speaking to Britain's Sunday Times last month, Gomez said her relationship with Bieber exposed her to a large amount of public scrutiny.

"I didn't think I was doing anything bad by falling in love," she said.

"There's such an emphasis on people being the perfect thing and then destroying them because it's good press. Throw in the fact that you're a teenager­­­­ – it makes it more difficult."