Jessica Simpson was left red-faced after accidentally blurting out her unborn baby's gender in a "crude" chat during a U.S. Tv interview on Wednesday (06Mar13).

The singer-turned-reality Tv star was discussing the difficulties of her second pregnancy on late-night show Jimmy Kimmel Live! when she let slip she is expecting a son.

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

After realising she had let out her big secret, the Fashion Star mentor said, "Well, I guess I just told the world I'm having a boy."

Kimmel then quipped, "Oh, I didn't even know it was that. I thought maybe you were having a girl with a penis."

Simpson added, "I can't believe I did that; that was not planned... I just did it so crude, too; that was awful. I'm talking about wieners."

Rumours have been circulating suggesting Simpson and her fiance Eric Johnson are expecting a baby boy to join their daughter Maxwell, but the blonde beauty admitted she had no idea how the information leaked.

She joked, "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. (Maybe) they call up people, tell their parents, and the parents talk about it at the grocery store. Who knows?"

Simpson's daughter Maxwell was born last May (12), while her second baby is due this summer (13).