Bloated “BORN THIS WAY” singer sparks fears she has debilitating lupus.

LADY GAGA has packed on a whopping 28 pounds – and now pals fear friends fear the pop star’s weight gain is due to a life-threatening medical condition!

The 26-year-old singer has a family history of the auto-immune disease lupus, and insiders worry she’s secretly taking medication that’s caused her to blow up like a balloon.

“Gaga usually weighs about 100 pounds, but since she began her ‘Born This Way Ball’ tour in Korea in late April she’s put on 28 pounds,” revealed a friend.

Fans gasped in shock when the petite 5-foot-1 singer, who’s known for her outrageous costumes, flaunted her fuller figure in Amsterdam on Sept. 17. Her butt cheeks were spilling out of her fishnet tights, and her waist had a roll of flab.

The ENQUIRER previously reported that Gaga gained 10 pounds thanks to late-night food binges with her soon-to-be-fiance, actor Taylor Kinney. And she recently admitted that she put on “like, 25 pounds,” in part because the self-professed “New York Italian girl” can’t resist pigging out on pasta and pizza.

But insiders worry that her weight gain has been accelerated by a battle with lupus, said the friend.

Lupus causes the body’s immune system to mistakenly attack healthy tissues and can affect the skin, joints, kidneys, brain and other organs. It also leads to an increased risk of heart attacks in women.

“Two years ago, Gaga admitted on Larry King’s show that she tested borderline positive for the disease,” said the source.

“She said she wasn’t showing any symptoms, but her aunt Joanne died from lupus and the steroids prescribed to help keep the condition in check can easily lead to extra weight.

“That’s why everybody is so worried about Gaga’s sudden weight gain. She’s always been obsessed with her appearance, so you know that something is terribly wrong.

“But one thing about Gaga – she’s a fighter. Whatever she’s facing, she’lldo everything in her power to beat it.”