For the bash, thrown at Poppy in West Hollywood, Calif., the 36-year-old singer sported a shiny black jacket, worn as a dress, paired with pointy thigh-high stiletto boots. The look was completed with a blond ponytail wig and a black headpiece.
During the festivities, the former “Destiny’s Child” hitmaker mingled with Jessica Alba, who appropriately went as Juno from the 2007 Ellen Page film of that name.
The expectant mother — who just revealed she’ll be having a son — wore a striped T-shirt, a camo hoodie, jeans and ankle boots with orange laces. Meanwhile, husband Cash Warren rocked a Luigi costume and white Reebok sneakers.
Elsewhere, Beyoncé dressed as Lil’ Kim from Missy Elliott’s “The Rain” video, and Jay-Z channeled the late Biggie Smalls in a red leather jacket.
A$AP Rocky was also spotted stepping out for Rowland’s party. Sans costume, the rapper opted for Vans Old Skool sneakers with yellow laces instead.