Billie Eilish wore Oscar de la Renta at the Met Gala under one condition: They stop using fur

Billie Eilish stunned in a peach gown with a long train that cascaded down the steps of the Met Gala on Monday night — and her Marilyn Monroe-inspired look came with some conditions for designer Oscar de la Renta. The fashion house is going completely fur free, per Eilish's request.

"It was an honor to wear this dress knowing that going forward Oscar de la Renta will be completely fur-free!!!!" Eilish, who co-chaired the gala, wrote on Instagram, sharing shots of the stunning dress at the fashion gala. 

The 19-year-old said she is beyond thrilled that creative directors Fernando J. Garcia and Laura Kim, as well as the whole Oscar de la Renta, team heard her on this issue "and have now made a change that makes an impact for the greater good, not only for animals but also for our planet and environment too."

"I'm honored to have been a catalyst and to have been heard on this matter," her post continued. "I urge all designers to do the same."

Eilish often uses Instagram to speak out against the use of fur and animal cruelty, and last year, her music appeared in an anti-fur campaign by Fur Free Alliance.

While Eilish's old Hollywood glamour look fit in with the Met Gala theme – "In America: A Lexicon of Fashion" – her animal activism fit in with the event's repast. All the food served at the gala, which is a star-studded fundraiser for the Fashion Institute – was vegan.

When it was announced in August that this year's Met Gala would serve an all-vegan menu, PETA President Ingrid Newkirk said she hoped the celebrities attending would also be mindful of animal activism. 

"PETA is celebrating the end of the Meat Gala and hopes to see attendees embrace Earth- and animal-friendly fashion, too—meaning no fur, leather, cashmere, wool, or feathers," Newkirk said.

After the event, PETA commended Eilish, one of its 2021 Most Beautiful Vegans, for making a change with her Met look. CBS News has reached out to Oscar de la Renta for more information and is awaiting response.