New York, New York - Euphoria star Sydney Sweeney became nearly unrecognizable while filming her new biopic, and she's now spilling the secrets behind her dramatic transformation.

The 27-year-old recently took on the role of professional boxer Christy Martin in a biographical film due in theaters this fall.

As she revealed in an interview with W Magazine, Sydney took on a rigorous fitness routine to prepare.

She followed a strict plan that included an hour of strength training every morning, two hours of kickboxing at lunchtime, and another hour of strength training in the evening.

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"My body was completely different," Sydney said. "I didn't fit in any of my clothes."

After following the routine for three and a half months, the Anyone But You actor gained about 30 pounds, further accentuating her famous curves.

"It was crazy! I was like, 'Oh my god,'" she said."But it was amazing: I was so strong, like crazy strong."

But the transformation went beyond just her physique, as Sydney also rocked brown eye contacts and had her hair styled in a brunette, '80s-style tousled bob.

Sydney's dramatic new look didn't last long, though, as she had to shed the weight in just a few weeks as she returned to the set of Euphoria for the show's long-awaited third season.