Ashlee Simpson's latest gig is modeling for the fall campaign of her big sister Jessica Simpson's clothing line. 

While Jessica has taken a break since the birth of her son Ace Knute Johnson on June 30, Ashlee has filled in and is determined to make her sister proud. 

In the exclusive behind-the-scenes video from the shoot, obtained by E! News, the gorgeous blond is taking advantage of the spotlight, by showing off her toned figure in a variety of chic-bohemian-inspired clothing and accessories that match her style. 

The 28-year-old singer will model clothing, accessories and shoes from the Jessica Simpson Collection Fall 2013, in a series of advertisements out later this month.

See photos of Ashlee here:

Ashlee is also the co-creative director of Jessica's youth line, Jessica Simpson Girls, and she revealed to Life & Style magazine Thursday that she has own fashion ambitions.

"It will be adult. It will definitely [be different from Jessica's,] she told the publication. "I think there's a time and a place for certain outfits, and for me, it's also about comfort and kind of finding your own way with clothes," she said. "Knowing there is a time to mix and match and what mixes and matches [is always important]. It's always good to try, though!"

Meanwhile, on a personal level, Ashlee was spotted with rumored boyfriend, Evan Ross in NYC on Tuesday. 

With dating rumors swirling for nearly a month, the 24-year-old son of Diana Ross supported Ashlee at the launch of the Jessica Simpson Fall 2013 Campaign, which she was held at Above Allen. 

The two helds hands  and posed in pictures together.  Simpson looked beautiful in a turquoise dress, while Evan, wore a gray suit jacket over a deep V-neck shirt.

"Evan and Ashlee have been friends for a really long time, probably ten years," a source told Us Weekly. "They know each other from the club scene and have tons of mutual friends." 

Tags: Ashlee Simpson Jessica Simpson