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(Yahoo!) - You never know exactly what will come out of Jessica Simpson’s mouth … and neither does she!

While appearing on “Jimmy Kimmel Live” Wednesday, the mom-to-be let it slip that she and her fiancé, Eric Johnson, are expecting a son.

“I never knew that a wiener could actually make me so nauseous,” the 32-year-old queen of the loose lips said when the talk show host asked how she was feeling during her second pregnancy. She then burst out laughing and covered her mouth with her hand.

“Wait … what did you intend to say there?” Kimmel asked her.

“Well, I guess I just told the whole world that I’m having a boy,” Simpson replied with a smile.

“Oh – I didn’t even know what was happening,” Kimmel laughed.

As the audience cheered, the “Fashion Star” went on to say that luckily had already confided to her family and friends that she has a boy on the way – and she was glad she did!

"I can't believe I did that," she said about her accidental admission. "That was not planned."

When Kimmel brought up the report in Us Weekly that the baby will be named Ace, she didn’t deny it. She just giggled – a lot.

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