Gigi Hadid kept her pregnancy private for a few months before confirming the news -- all thanks to a fashion trick.

The 25-year-old supermodel recently told a fan in the comments section on social media that specific clothing acts as an optical illusion.

The fan asked: "How do you not have a tummy?" Hadid wrote back, "This angle and the really baggy jumpsuit make for an optical illusion. From the side, it's a different story!"

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Gigi Hadid attends the WARDROBE.NYC launch of Release 04 DENIM & Levi's® Collaboration on July 17, 2019, in New York City. (Photo by Ilya S. Savenok/Getty Images for WARDROBE.NYC)

Gigi Hadid attends the WARDROBE.NYC launch of Release 04 DENIM & Levi's® Collaboration on July 17, 2019, in New York City. (Photo by Ilya S. Savenok/Getty Images for WARDROBE.NYC)

In April, the Vogue cover star confirmed she's expecting her first child with boyfriend Zayn Malik, 27, during an appearance on "The Tonight Show starring Jimmy Fallon." The baby is reportedly due in September.

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"Obviously, we wished we could have announced it on our own terms, but we’re very excited and happy and grateful for everyone’s well wishes and support,” Hadid said.

She continued: “Especially during this time, it’s a nice silver lining to be able to be home and be together and really experience it day by day.”

The star also revealed her current craving: everything bagels. "I eat an everything bagel a day," she said.

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The couple has been quarantining together on her family's farm in Pennsylvania since the coronavirus outbreak in March.

A source told People magazine that Hadid and Malik are "thrilled" about the baby.

"They've been through their ups and downs, but neither stopped caring about the other," the source said in May. "They've jumped on the timing of having a baby and are preparing for their new lives."