(Cover) - EN Star Style - Jessica and Ashlee Simpson are set to design a "tween" collection.

The sisters will create the clothing line as part of the successful Jessica Simpson Collection.

Jessica, whose fashion empire is estimated to make $1 billion in sales this year, says she is excited for her younger sibling to join the project because her "savvy rocker" style will appeal to a younger audience.

"Creating a tween apparel collection was a natural extension for the brand," Jessica told WWD. "I'm excited to bring my sister, Ashlee, along as co-creative director of this division, because she brings a savvy rocker edge that defines today's tweens."

The line will debut later this year and will include sportswear, denim and activewear. It will feature knit tops, hoodies, pullovers, graphic T-shirts, drawstring pants and footwear.

Ashlee, 26, has revealed she is looking forward to "inspiring" young girls through fashion.

"My goal as co-creative director will be to design clothes that will help inspire young girls to express their personalities and creativity through fashion," she said.

Jessica already has a highly successful fashion empire. The 30-year-old blonde beauty launched Jessica Simpson Dessert by Jessica Simpson in April 2004 which included edible perfume, lip gloss and other beauty products under the Dessert Beauty brand. A parallel line named Dessert Treats was launched the following year. Jessica has also created the Jessica Simpson Collection in which she designs and markets a line of handbags and shoes and boots.

The stunning star also has a fragrance line including her debut scent Fancy, Fancy Love and Fancy Nights. (C) Cover Media