Nicole Kidman's rigorous butt workout described by her costar as 'epic' and 'awful'

Nicole Kidman likes to feel and share the burn.

During an appearance on "The Tonight Show with Jimmy Fallon" on Monday, Kidman's "A Family Affair" co-star Joey King spoke about what she had learned from working with the Academy Award-winning actress on the Netflix film, which also stars Hollywood heartthrob Zac Efron.

"They're both like so hot," she told Fallon of the actors, 57 and 36, respectively. "They're like the fittest people I've ever met, so, I was inspired by them. So I became a bit of a, you know, tubular gym rat on the set."

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"[Nicole] taught me like the most epic, awful butt workout I've ever learned in my life," she said. "I was like, ‘I’m a youngster. I can hang…I'm agile.' I thought I could hang, but I couldn't hang," King, 24, admitted.

"It was all these donkey kicks, and the rainbows, and you know, the fire hydrants," she said, listing the descriptive names of popular exercises. "But you have to keep your leg in the air for like 12 years. It's so hard."

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King said since filming, she has incorporated the arduous routine into her own workout, because "it's the most effective," and she added that she often texts Kidman pictures, joking she should "call an ambulance."

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In an interview with the Los Angeles Times, Kidman previously explained why incorporating a variety of different exercises was ideal for remaining fit.

"If you think you are going to wake up and run five miles every morning for the rest of your life, you’ll get bored and hit the snooze button after a week. So I try and mix it up with sports, running, yoga and even just going for a walk with my husband and the kids. Living in Nashville makes this easier, as it’s so nice just being outside," she explained. "I also love spinning. I try to get everyone to spin."