The Real-Life Inspiration Behind Caitlyn Jenner's 'Vanity Fair' Hair

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Caitlyn Jenner's hair looks absolutely fabulous on the cover of Vanity Fair, but she can't take all the credit.

Vanity Fair's Fashion and Style Director Jessica Diehl revealed to ET that it was supermodel Cindy Crawford's mane that they used for inspiration for Caitlyn's loose wave hairstyle in the magazine.

"Cindy just has great, effortless hair that always looks glamorous and doesn't look too done. She is a glamazon," Diehl told ET.

WATCH: 'Vanity Fair' Stylist on Dressing Caitlyn Jenner: 'Everything Looks Good on Her' 

When Cindy got word that the 65-year-old former Olympian "borrowed her hair," she complimented Caitlyn's legs!

NEWS: Jon Stewart Slams Caitlyn Jenner Media Coverage: 'Welcome to Being a Woman in America' 

While Caitlyn's luscious locks may be a stylist's dream to work with, her shoe size presents more of a challenge.

"She is so proportionate and yes a size 13 shoe, difficult to find," Diehl admitted. "But I think maybe we'll get lucky now and the Paul Andrew and Tabitha Simmons of the world and Manolo Blahnik will suddenly start making size 13s -- you never know."

Caitlyn's life as a transgender woman will be seen in I Am Cait, E!'s eight-part, on-hour documentary series. The first promo was released on Wednesday.

I Am Cait  premieres Sunday, July 26, at 9 p.m. ET/PT. Watch the promo below.

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