Jessica Simpson has no issue poking fun at her fluctuating weight throughout her career.

The 36-year-old singer recently sat down with CBS Sunday Morning to talk about her incredibly successful fashion line, The Jessica Simpson Collection, and why creating a full size range is especially meaningful to her.

"It's very important for me to let every woman feel included," Simpson said. "Like, every person needs to feel included. If I make a shirt, I'm going to make sure every size is available. Because I have been every size, trust me."

WATCH: Jessica Simpson Flaunts Curves on Date Night With Eric Johnson

Of course, Simpson is getting the last laugh at her critics. She's successfully kept the weight off since her latest pregnancy with son Ace in 2013, and has no problems showing it off.

The mother of two also talks about constantly being underestimated when it comes to her best-selling collection. Simpson says that she and her mother, Tina, are involved in every step of the design process, and that each piece must get the stamp of approval before she puts her name on it.

"People are shocked that they like my brand," Simpson admits. "Maybe 'cause it's not that expensive? Or maybe because I was a cheesy pop star back in the day. I have no idea."

Simpson's appearance on CBS Sunday Morning airs this Sunday at 9 a.m. on CBS.

WATCH: Jessica Simpson Looks Better Than Ever in New Clothing Campaign

ET spoke to Simpson earlier this month in her hometown of Waco, Texas, where she invited us for a ride-along to her Jessica Simpson Collection charity event at Dillard's. When asked what her secret is to body confidence, Simpson was candid as always.

"Sex," she answered bluntly.

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