Underwear is having a fashionable moment.

Sydney Sweeney stepped out at the 2023 Cannes Film Festival in a bustier slip dress — wearing her engagement ring for the first time in a year — while with her fiancé as the couple was photographed leaving the elegant Hotel Martinez.

On Sunday, the “Euphoria” star, 25, bared her cleavage in a plunging white spaghetti strap slip dress, which showed off an exposed blue satin Miu Miu bra ($775) peeking out from underneath the cups. 

Sweeney paired the long white gown with matching platform sandals, leaving her blond hair down in loose waves and other jewelry minimal. 

On TikTok, some fans wondered if she was having a wardrobe malfunction because her bra was so exposed.

“What’s going on with the dress malfunction in [sic] this beautiful girl,” a commenter questioned. 

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Others thought the dress seemed to be staying put. “I aspire to her level of trust in the dress,” another person wrote. 

Someone explained the dress only appeared to be falling off “because when you have a naturally fuller bust it’s impossible to find clothes that fit your body and fit your chest,” adding, “She’s making the best of it.”

Others didn’t have an issue with the plunge, they simply didn’t like the style. “Her stylist did her dirty,” one TikTok commenter declared. 

Sweeney’s main accessory was her engagement ring and the arm of fiancé Jonathan Davino.

The couple tends to be tight-lipped about their relationship, with the “Everything Sucks” actress frequenting the red carpet solo since they got engaged last year.

Sweeney, 25, sparked relationship rumors with Glen Powell while they filmed the upcoming romantic comedy, “Anyone but You” in Australia.

Despite the rumors — and saying she lived her “best life” with Powell — the actress stepped out for a date night with her 38-year-old beau at Sake No Hana in New York City in matching leather ensembles earlier this month.