Jessica Simpson is celebrating her fitness accomplishments by slipping into a little black dress! The designer took to Instagram on Friday to show off her svelte figure, posting a behind-the-scenes photo of her new Weight Watchers commercial shoot. "Too proud to sit down!!" she wrote in the caption. Jessica struck a confident pose for the snap, placing her hands on her hips and holding her chin high. The mother of two has been vocal about her weight-loss journey since giving birth last year to Ace, Jessica and fiancé Eric Johnson's son. In an interview with POPSUGAR Fitness earlier this month, the star's longtime trainer, Harley Pasternak, showed us Jessica's workout routine.