The 42-year-old nabbed a spot in PEOPLE's Most Beautiful issue -- here's why!

Science hasn’t proved it yet, but we have a theory Gabrielle Union is aging backward, Benjamin Button-style. (Maybe that’s why brands like Neutrogena and SensatioNail clamor to feature the star in their campaigns.) But all jokes aside, when it came to narrowing down PEOPLE’s annual World’s Most Beautiful list, including the actress was a no-brainer. Read on to find out how she radiates beauty — both inside and out.

PASADENA, CA - FEBRUARY 06: Actress Gabrielle Union

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While we happen to think Union stuns in everything she wears (see examples here, here and here), according to the star, there’s one piece (technically, two pieces) in her closet that gives her the confidence to do just about anything: a stylish Roberto Cavalli “Rio-cut” bikini.

“It’s like a magic bikini, like The Sisterhood of the Traveling Pants — if I could give this bikini to everyone I know, of all shapes and sizes, [I would],” she told PEOPLE. “I don’t know what it is; I get a little extra bounce in my step [when I wear it].”

But that confidence didn’t come over night. “It has come with age — age and continuing to read and travel and realize that nobody, except for mean girls, gives a s–t about a dimple in a thigh or what your upper arms look like,” Union revealed. “If you carry yourself with confidence, and you move through the world with your head held high and your shoulders thrown back, you don’t need to be a [size] double-zero. What people are attracted to is the fact that you’re attracted to yourself.”

Which is why the 42-year-old is quick to remind her friends that basing their self-esteem on a teen’s thigh gap “is a little bizarre.”

“[My friend and I] were having this discussion the other day, somebody was like, ‘Uh, if I could just look like Kendall Jenner!” she told PEOPLE. “I’m like, ‘Kendall Jenner is 12 years old [laughing], you are 44. Clearly you are going to need some other role models. You are going to kill yourself in an attempt to look like a child! It’s okay for Kendall Jenner to look like Kendall Jenner, and it’s okay for you to be fly and amazing and fit and a healthy 44-year-old woman.’ It’s okay to have a range of beauty ideals.”

So, who does the actress consider her beauty icons then? “I have a few, and they change daily depending on who I’m stalking on Instagram,” Union confessed. “I would say, just in life, I’ve always looked to Diahann Carroll. She’s still delicious, sassy and confident and the epitome of beauty and grace and sizzle.” Of course, she couldn’t leave out the Queen. (Bey, that is.) “Some days it’s Beyoncé, some days it’s Rihanna, some days it’s Jamie Chung, some days it’s Jessica Simpson — it just kind of depends where my head is at,” she said.

She also looks to everyday icons for inspiration, such as the moms who frequent her local gym. “They come in harried, drop their kids off and you see them get Zen in the workout class — they’re strong, fit and amazing,” she said. “And then they grab their kids and the kids hug them, and you’re like, ‘Those are dope women.'”

What do you think of Gabrielle’s advice? Do you have a piece in your closet that makes you feel extra-confident? What is it? Share below!

–Sarah Kinonen

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