Credit: Gregg DeGuire/FilmMagic

When Jessica Simpson tunes in for the premiere of NBC's Fashion Star March 13, her body won't look anything like it does now.

"I wasn't pregnant when we shot it. It will be amazing to see myself with a waistline," the 31-year-old said during a conference call Thursday. "I'll be like a big blob sitting on the couch watching myself thin."

Simpson will mentor 14 contestants alongside fellow fashion designers Nicole Richie, 30, and John Varvatos; supermodel Elle Macpherson, 47, will host.

"Teaming up with this show was a perfect fit," Simpson said. "I couldn't turn it down because I felt like it was great for my collection, but it was also important for me to talk to these up-and-coming designers and mentor them and kind of show them the ropes and really try to lead them in the right direction."

Now that she's expecting her first child with fiance Eric Johnson, Simpson said she's thinking of creating a maternity line for the Jessica Simpson Collection.

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"The point of launching a maternity line, for me, is to do something different," Simpson explained. "I'm not buying any maternity clothes. I'm wearing all clothes that come in bigger sizes. I really want to make a maternity line that's comfortable, but really stylish for people, because I believe that we all deserve to feel good and look good."