Selena Gomez is being treated for lupus

Selena Gomez is being treated for the serious disease of lupus, according to her grandfather, but is doing well.

The word comes just as Gomez, 21, has returned from Nepal where she visited as a UNICEFambassador to bring attention to children in need.

Radar, followed by Hello magazine, is reporting that her grandfather, Ricardo Gomez, of Grand Prairie, Texas, who helped raise her, confirmed she was diagnosed several years ago.

"She's in treatment," he told Radar. "She's getting along pretty good."

Lupus is an autoimmune disease in which the body's immune system attacks normal, healthy tissue, for still mysterious reasons. It can be life-threatening.

Selena's various issues, including her tumultuous relationship with Justin Bieber, her stint in rehab and her punishing work schedule, have exacerbated her struggle with the disease, her grandfather says.

"What worries (us) more," he says, "is that she doesn't know how to say no. She won't take time for herself to relax, to eat well."

Bieber, by the way, is not a hero to her grandparents, not any more.

"He was just a nice little fella," Ricardo says. "Totally different from what he is right now. … It just makes me feel upset because he used to be a real nice boy."