Blake Lively has always been stylish, so it’s no surprise the actress played a major role in designing the gorgeous costumes in the timeless romantic fantasy drama The Age of Adaline.

In the film, Lively plays Adaline, who has remained 29 years old for eight decades, never getting close to anyone for fear they’ll discover her age-defying secret. That is, until she meets the charismatic Ellis (Game of Thrones’ Michiel Huisman).

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Because the story lent itself to multiple time periods, it was an opportunity for Lively and the team to create something visually spectacular – but also to accurately depict what an everyday woman would wear.

“The honesty in it, the history in it was really important because we could’ve actually had even more fabulous costumes if we were just purely making a movie from a wardrobe perspective,” Lively says in ETonline’s exclusive look at one of the special features. “But we really wanted to be honest and true, and what would this woman be able to actually afford?”

“Now being an amalgamation of all these different decades was a really neat thing,” she adds. “Ellis takes notice of her immediately when he sees her, and with Ellis, you see her loosen up, you see her become more contemporary [in her wardrobe choices].”

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Director Lee Toland Krieger marveled at Lively’s contribution to the costume design, saying that she “really deserves the credit.”

While promoting the movie back in April, the fashionable mom revealed that she has been saving clothes since she was a teenager for her future daughter.

“Since I’ve been 16, I’ve been like, ‘My child will love this piece from Forever 21,’” Lively, who turns 28 on Tuesday, told ET at the time. “They’re never going to want it, but that’s why I’m happy to have had a girl because I have a lot of things I’ve been hoarding with the excuse to pass it down to her.”

Considering how flawless Lively looked earlier this year in a stunning red leather-and-lace gown and see-through body suit from Monique Lhuillier at Age of Adaline’s New York City premiere and afterparty, we’d love to take a peek at her closet.

The Age of Adaline arrives via digital HD on Tuesday, before going On Demand on Sept. 4. On Sept. 8, it'll hit shelves on DVD and Blu-ray.

Earlier this summer, Blake Lively rocked the sheer trend. Press play below to find out more on her stylish look!