It's been almost a decade since we witnessed Jessica Simpson and Nick Lachey's marriage first-hand on the hit show "Newlyweds." Even though the two have both happily moved on since they decided to get a divorce in 2005 after just three years of marriage, it wasn't until now that Simpson decided to open up about a big mistake within that relationship.

As a 35-year-old fashion mogul, who is celebrating the 10th anniversary of her $1 billion fashion line this week, she believes the worst financial decision she ever made was marrying Lachey.

"The biggest money mistakes? I don't know. For some reason I thought of my first marriage," she said when asked about the mistakes that have helped her grow on CNBC's "Closing Bell" on Thursday.

"That's actually a common answer believe it or not," Host Kelly Evans said in response.

Years after their divorce, Simpson went on to have two children, Maxwell Drew, 3, and Ace Knute, 2, with her husband, former NFL player Eric Johnson, according to People. Lachey also remarried and had two children, Camden John, 2, and Brooklyn Elisabeth, 8 months, with his wife Vanessa Lachey.

Just last year, Lachey, 41, opened up about his relationship with Simpson, and it turns out he is really happy they never decided to have children.

"In our situation, that was probably the best thing that could have ever happened, that we didn't have kids," he said on SiriusXM. "All things being equal, it was the best thing probably for both of us, that we went on with our lives."

While the two are very happy with their current situations, Simpson believes she is done having children. "No more kids on the horizon," she told Entertainment Tonight earlier this week. "That would freak me out a little bit."