On Wednesday's edition of ABC's "Jimmy Kimmel Live!," pregnant Jessica Simpson inadvertently revealed she's expecting a boy.

While discussing how her second pregnancy has been more difficult than her first, including more vomiting, she blurted out, "The crazy thing is, I never knew a wiener could actually make me nauseous."

After disclosing the baby's gender, she said, "Well I guess I just told the world that I'm having a boy!" Host Jimmy Kimmel, who initially didn't realize her slip-up, joked, "I didn't even know what was happening…I thought maybe you were having a girl with a penis."

Simpson later said, "I can't believe I did that. That was not planned."

PHOTOS: Jessica Simpson Through the Years

When Kimmel asked her about the rumors that she'll name the baby Ace, she attempted to backtrack by declaring, "Let's hope it's a boy!"

Simpson and fiancé Eric Johnson welcomed daughter Maxwell Drew Johnson last May. She announced her latest pregnancy last Christmas Day.

Kate Middleton also may have also accidentally revealed the sex of her baby this week.

According to The Daily Telegraph newspaper, Middleton was talking with a member of the public on a visit to Grimsby when she was presented with a teddy bear.

Sandra Cook, who was standing in the crowd next to the gift-giver, told the Telegraph that she overheard Middleton's response.

"I distinctly heard her say 'thank you, I'll take that for my d …' then she stopped herself. I said to her: 'You were going to say daughter weren't you?' and she said, 'No, we don't know'," Cook, 67, told the Telegraph.

""I said, 'Oh I think you do', to which she said: 'We're not telling'," Cook added.

There has been growing speculation about the baby's gender. A South African genetic expert has even created drawings of how she believes the unborn child could look as a toddler and teenager.

PHOTOS: The Life and Times of Kate Middleton

(ABC)