Lili Reinhart is opening up about the heartbreaking reason she hated one of her biggest red carpet looks.

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The actor, who has become one of Hollywood's most outspoken critics of unrealistic beauty standards, made the comments in a new interview with Cosmopolitan, where she discussed how limited sample sizes affect actors' red-carpet appearances.

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"Stylists aren’t given racks of clothes for people who are above a size 4 [UK size 8]," Lili explained.

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She then recalled how she once attended a Vanity Fair Oscars party in a dress she never actually wanted to wear — just because it was the only one available that fit her.

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"I went to the Vanity Fair Oscars party one year wearing the only dress that fit me on the rack, and I was deeply unhappy with how I looked because I didn’t want to wear that," she said.

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Although Lili didn't specify which look she was talking about, she has attended the annual event twice.

In 2020, she wore a voluminous floral gown with sheer mesh detailing, puff sleeves, and a dramatic flared skirt.

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In 2022, she donned a glamorous, dark red sequined dress with a plunging neckline and fitted silhouette.

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In the past, the actor has been extremely open about the impact Hollywood beauty standards have had on her.

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In 2022, she famously called out Kim Kardashian after Kim revealed she had lost 16 pounds in three weeks to fit into Marilyn Monroe's dress for the Met Gala, criticizing her for the potential harm to others.

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"The ignorance is other-worldly and disgusting," she wrote on Instagram at the time. "Please stop supporting these stupid, harmful celebrities whose entire image revolves around their bodies."

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She later added, "I am not generally an angry person but I swear to god, the toxicity of this industry sometimes really gets to me. And I have to do my little Instagram-story rants to release my rage."

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The same year, Lili also shared that she had been "struggling with obsessive thoughts" about her body and weight for months, saying on Instagram, "I didn't think being in this industry, that is so obsessed with women's bodies and weights, could ever mess with my own body acceptance and positivity. But it has. I wish I hadn't grown up in a time where the media worshipped only one size of women."

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Reflecting on where she stands today, Lili told Cosmopolitan that it's "really difficult" to live in a culture that seems to have moved away from body positivity, but she tries to tune out the pressure. "I’m living in my own body," she said. "I’m just trying to be present with it, I guess."

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Read her full interview here.