Just in time for Halloween, Nicole Richie dressed up in lace cat ears and flaunted her cleavage in a plunging black dress at a red carpet event on Oct. 24. Credit: Jon Kopaloff/FilmMagic

Halloween couture? Nicole Richie dressed up in a Catwoman-inspired ensemble at the Who What Wear and Cadillac's 50 Most Fashionable Women of 2013 event on Thursday, Oct. 24. The 32-year-old fashion designer walked the red carpet wearing cat ears and a sexy black dress at The London Hotel in West Hollywood.

Richie showed off her skinny body and flaunted some cleavage in a plunging black Dilek Hanif dress, which featured sparkly embellishments and fringe. She also styled black Robin's Jean pants underneath, Christian Louboutin heels and carried a nude House of Harlow 1960 clutch. To top off the ensemble, Richie donned a black lace cat ear headpiece and wore cat-eye liner.

Although the mom of two -- daughter Harlow, 5, and son Sparrow, 4 -- looked gorgeous, a source told Us Weekly that she was battling the flu that evening. For support, she brought younger half sister Sofia Richie, 15, to the event with her. She also posted a photo of the two posing together with celeb pal Jessica Alba on Instagram.

"On my way to @Cadillac's #StyleDriven event to celebrate @WhoWhatWear's 50 Style Stars with @jessicaalba and @sofiarichie1," she captioned the shot. Sofia also posted a photo of her and her sister posing in black fur coats before the event and wrote, "Fashion night with my best friend."

Tell Us: What do you think of Richie's Catwoman-inspired ensemble?