Selena Gomez wasn't in rehab, she was undergoing chemotherapy.

“I wanted so badly to say: ‘You guys have no idea. I’m in chemotherapy. You’re assholes’.”

Late in 2013, pop star Selena Gomez cancelled the Australian and Asian leg of her world tour. A few months later, she checked herself into a rehab centre.

Typical, right? A young star breaks up with her boyfriend (Justin Bieber) and can’t cope with the public scrutiny and media attention that follows, so self-medicates only to wind up in rehab when she’s supposed to be performing.

And thus, many of the tabloids speculated that Gomez was undergoing treatment for “addiction problems”.

Gomez didn’t have a substance abuse problem though, she was actually undergoing chemotherapy for the auto-immune condition lupus.

“I was diagnosed with lupus, and I’ve been through chemotherapy. That’s what my break was really about,” Gomez told Billboard magazine in a recent interview.

“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.”

Lupus is a chronic condition where the body’s immune system becomes hyperactive and essentially attacks itself, trying to destroy health tissue.

It can lead to the destruction of the kidney, heart, brain, spine, and lung tissue.

“I could have had a stroke,” she says.

The cause of lupus is unknown and the symptoms vary widely between individuals with the disease — what is known, is that it affects almost 5 million people world wide.

Women are also significantly more likely to have the condition.

Some of the most common symptoms of the illness include rashes, fever, fatigue, body aches and pains and hair loss.

It is currently treated by a mix of drugs and by chemotherapy designed to suppress the action of the immune system.

In the same interview, Gomez criticised the media’s handling of her stay at the Dawn at the Meadows rehab facility as well as their ongoing treatment of her relationship with Justin Beiber.

“I’m so f—ing nice to everybody, and everyone is so vile to me,” she said.

“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.”

Want more of Selena Gomez? Here are some great pics from her Instagram: