By Selena Hill (staff@latinospost.com) | First Posted: Mar 07, 2013 04:02 PM EST

Oh boy, Jessica!

During an interview on Wednesday's "Jimmy Kimmel Live!," the "Fashion Star" mentor accidentally blurted out that she and her finance Eric Johnson are expecting a baby boy. Her first hint at the baby's gender went unnoticed by Kimmel and the live studio audience--it wasn't until she said it again a second time that gave the secret away.

The conversation started when the 32-year-old singer and reality star began talking about how it feels to be pregnant for the second time around.

"Oh my gosh, it's a total different pregnancy, I just feel awful," said Simpson on the late night talk show. "I've been vomiting and the crazy thing is I never knew that a wiener could actually make me nauseous."

That's when she took a pause to think about what she just said and went on to say, "Oh, shoot, I guess I just told the world that I'm having a boy!"

Kimmel, however, didn't catch on until she blurted it out: "Oh! I didn't even know what has happening," he laughed, admitting that he didn't realize her "wiener" comment meant something else completely. "I thought maybe you were having a girl with a penis!"

"I kind of just outed that I'm having a boy right?" she said. "I can't believe I did that, that was not planned."

The fashion designer also confirmed that rumors that she is considering to name her second child "Ace" are true.

She and her ex-NFL star finance had a baby girl named Maxwell in May 2012 and have been engaged since November 2010.

Watch a video clip of the interview below.