Jessica Simpson Accidentally Reveals Second Baby's Gender on 'Jimmy Kimmel Live'

Jessica Simpson Dillards - P 2012
Getty Images

Jessica Simpson Dillards - P 2012

"I can't believe I did that; that was not planned," the "Fashion Star" mentor says of the "crude" way she let the news slip.

Jessica Simpson is having a boy, but you weren't supposed to know that yet.

While rumors have been circulating in the tabloids that the pregnant Fashion Star mentor is having a son, joining her 10-month-old daughter Maxwell, Simpson had yet to confirm the speculation -- until she accidentally blurted it out on Wednesday's Jimmy Kimmel Live.

PHOTOS: Reality TV Stars Turned Fashion Designers: The 6 Biggest Success Stories

During her appearance, Simpson began by telling Kimmel that her second pregnancy has been much more difficult than the first.

"I just feel awful, I've been vomiting," she said. "The crazy thing is, I never knew a wiener could actually make me nauseous."

She then caught herself and said: "Well, I guess I just told the world I'm having a boy."

At first, Kimmel didn't seem to realize what Simpson had revealed, saying: "Oh, I didn't even know it was that. I thought maybe you were having a girl with a penis," he quipped.

She said her family and friends knew, but admitted she had no idea how word got to the press that the baby was a boy, or that she apparently plans to name him Ace (she didn't confirm that to Kimmel, joking only that "let's hope it's a boy").

"I don't think that a lot of stuff people say is malicious in any way, but maybe I have some friends with some big mouths," she joked when asked how such information gets leaked. "[Maybe] they call up people, tell their parents, and the parents talk about it at the grocery store. Who knows?"

STORY: Jessica Simpson to Star in Semi-Autobiographical NBC Comedy

Throughout the interview, Simpson continued to seem surprised at her own slip.

"I can't believe I did that; that was not planned," she said, adding later: "I just did it so crude, too; that was awful. I'm talking about wieners."

As for when she and fiance Eric Johnson might walk down the aisle, Simpson added: "I keep planning on getting married, but I keep getting knocked up. It's just one of those things."

Jimmy Kimmel Live airs at 11:35 p.m. on ABC. Fashion Star returns for its second season at 8 p.m. Friday on NBC.