The 33-year-old singer turned fashion designer wore a form fitting canary yellow dress and white high heels to the event.
Simpson signed a Weight Watchers endorsement deal when she was still pregnant with her first child, a daughter named Maxwell, back in 2012. Simpson later became pregnant with her second child, a boy named Ace, who was born in the summer of 2013. Since then, Simpson has been working with the company to lose her pregnancy weight.
In a February Weight Watchers ad, Simpson showcased her 70-pound weight loss in a fitted black dress, joking that she was "too proud to sit down." In her following advertisement, revealed in March, the mother of two said she had a "newfound determination that I'm really proud of."