Katie Holmes and Jennifer Lopez have also opted in to the grown-up trend, so it's definitely a thing (whether you like it or not).

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Julia Roberts Elie Tahari Jumpsuit and Wolford Tube Top
Credit: Vivien Killilea/Getty Images

When I think of overalls, the children's label OshKosh B'gosh typically comes to mind, but that completely went out of the window once I saw Julia Roberts wearing a very grown-up version of the style.

VIDEO: InStyle Honors Julia Roberts as a Style Icon

The 51-year-old star proved that overalls have totally grown up in a sexy red design by Elie Tahari. Her one-piece is fresh off the runway — it made its debut last week at New York Fashion Week — so it's not available in stores just yet. But if you take a closer look, you may be able to see her little secret, which is up for grabs on the Neiman Marcus website. To nail the shirtless look without actually going shirtless, Roberts wore the Wolford Fatal Strapless Top in black ($120; neimanmarcus.com) underneath her overalls. It's a life-saver for outfits like these.

Katie Holmes, on the other hand, completely committed to the shirtless look. She took the grown-up trend a step further, wearing an open-back pair of overalls by Ulla Johnson ($297; mytheresa.com).

Katie Holmes Overalls
Credit: Felipe Ramales / SplashNews.com

If you're not ready to go topless, you could follow Jennifer Lopez's lead. Like Roberts, the singer showed a little skin by layering her Brunello Cucinelli overalls with a thin-strap bodysuit also by Wolford ($195; shopbop.com).

JLO Sexy Overalls
Credit: SplashNews.com

I'm not sure if I could pull off the grown-up overall look like Katie. But at least I know exactly what to wear underneath overalls, thanks to Julie and Jennifer's looks.