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Gigi Hadid shared some unknown tidbits about herself during a recent panel hosted by Reebok. In the event, where she joined other campaign spokeswomen from Aly Raisman to Zoe Kravitz, the model opened up about her health, and revealed that she was diagnosed with a thyroid disease.

The model said her medical condition, which she's been battling for two years, was actually the reason behind her recent drastic weight loss.

"My metabolism actually changed like crazy this year. I have Hashimoto's disease. It's a thyroid disease, and it's now been two years since taking the medication for it," the 21-year-old said.

Hashimoto's disease, in the simplest sense, is a condition where your immune system attacks your thyroid, according to Mayo Clinic. Hadid suggested that the treatment she's been taking for the illness has resulted in weight loss. In fact, when she was training for the Victoria's Secret Fashion Show, she focused more on building muscle than on shedding pounds.

"So for the VS show I didn't want to lose any more weight, I just want to have muscles in the right place, and if my butt can get a little perkier, then that's good," she said.

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Gigi Hadid walks the VS runway in 2016.

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Hadid walks the VS runway in 2015.

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Erica Gonzales is the Senior Culture Editor at ELLE.com, where she oversees coverage on TV, movies, music, books, and more. She was previously an editor at HarpersBAZAAR.com. There is a 75 percent chance she's listening to Lorde right now. 

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