TheFashion Star mentor unintentionally revealed her child's sex during a Wednesday night appearance on Jimmy Kimmel Live!.
"Oh my gosh, it's a total different pregnancy, I just feel awful," Simpson said when asked how she's been feeling since she started carrying fiance Eric Johnson's second baby. "I've been vomiting and the crazy thing is I never knew that a wiener could actually make me nauseous."
After a quick pause, Simpson yelled, "Oh, shoot, well I guess I just told the world that I'm having a boy!"
"Oh, okay! I didn't even know what has happening," Kimmel laughed, saying he thought her "wiener" comment was referring to something else. "I thought maybe you were having a girl with a penis! I don't know! Well, congratulations!"
"There's a report that says you're going to name your baby Ace," Kimmel said.
"Well let's hope it's a boy... Could Ace be a girl?" Simpson asked.
"I think so," Kimmel replied.
"[Well], I kind of just outed that I'm having a boy right?" the reality TV star noted, admitting she kind of negated her chances of playing games. "I can't believe I did that, that was not planned."
Reports that Simpson is expecting a boy have been circulating since January.
"It's Jessica's dream come true, she prayed she was having a boy," a source close to the Simpson family told RadarOnline at the time, adding that she and Johnson were already discussing potential baby names.
During Simpson's appearance on Jimmy Kimmel Live!, Kimmel tried to get to the bottom of how the news had already surfaced considered she was trying to keep the baby's sex under wraps.
"Does your family know you're having a boy?" Kimmel asked.
"Yes and all of my friends. It was kind of out and about in the press that I was having a boy. I was like, 'How do people know these things?'" Simpson wondered.
"Like how did people find out you were going to name your [10-month-old] daughter Maxwell?" Kimmel questioned, referring to how Maxwell's name had been leaked as well prior to her birth on May 1 of last year.
"I don't know," Simpson replied.
"Do you do like an investigation within your community of friends and stuff? Because there are only so many people you tell this stuff to, right?" Kimmel asked.
"Well, I don't ever think that a lot of the stuff that people say is malicious in any way, but maybe I have some friends with some big mouths, I don't know... I don't think they're calling up people or whatever, but maybe they tell their parents and their parents are talking about it in the grocery store and somebody, I mean, who knows how it all [happens]!" Simpson suggested.
"You need new friends is what it is. Your friends have loose lips," Kimmel joked.
Simpson also told Kimmel she's holding off on exchanging vows with Johnson until she's no longer pregnant -- and this time is most likely the last time she'll be sporting a baby bump.
"I keep planning on getting married but I keep getting knocked up," Simpson said. "[I] would like to stop being pregnant."
Simpson made the announcement she's expecting Johnson's second child in a Christmas Day tweet in which she posted a holiday photo of Maxwell sitting in the sand with "BIG SIS" written in the sand in front of her.
Simpson previously admitted the new pregnancy wasn't planned, as she was "extremely shocked" when she first found out she was expecting again.