Jessica Simpson may have made a costly mistake when she married Nick Lachey in 2002. "Extra" has learned that the music, fashion and TV mogul refused to sign a pre-nup.

Attorney Harvey Levin, managing editor of the entertainment Web site TMZ.com, told us that Nick, who was the bigger star at the time, actually drew up the pre-nup papers.

"This could literally end up costing Jessica Simpson a large fortune," Levin said. "Jessica clearly didn't anticipate she'd become a huge success during the marriage. Now we don't even know who the lawyers are in this case yet, it's early on. But if they end up going to court, he can get tens of millions of dollars that she earned."

Us Weekly reports that celebrity attorney Laura Wasser, who represented Angelina Jolie in her split from Billy Bob Thornton, will represent one side in this case. She didn't return our phone calls.

If the pair does divorce, Lachey would be entitled to half of everything Simpson made during the marriage, including the reported $35 million she raked in last year.

"This breakup has been in the pipeline for some time," said Us Weekly's Katrina Szish.

In this week's cover story, Us Weekly reports that Jessica e-mailed Nick the day before Thanksgiving telling him she was going to announce the split. Sources tell "Extra" that Nick had tried to work things out, and was ready to go with Jessica to visit her family in Texas, up until she told him the relationship was over.

"Nick's friends are saying he was completely surprised," Szish revealed. "Jessica's friends are saying she was involved in a fake marriage and really just needed for it to end."

And there's more bad news for all you romantics out there. When TV's "Newlyweds" first split, there was speculation that they might reconcile, but today, reports have them farther apart than ever.

"Obviously it's finally over," Szish said.