01/11/2011 08:46 GMT | Updated 31/12/2011 10:12 GMT

Jessica Simpson Confirms Hollywood's Worst Kept Secret - Baby On Its Way

Jessica Simpson has confirmed the obvious - she's having a baby.

The 31-year-old entertainer tweeted a photo of herself dressed as a mummy for Halloween, holding her baby bump with the words, "It's true. I am going to be a mummy."

It will be the first child for Simpson and her fiance Eric Johnson. The two announced their engagement last year.

Her pregnancy has been rumoured for weeks, and recently, photos of Simpson - with a bulging bump - have appeared.

Pregnancy won't slow Simpson down. She's signed up to be a mentor on the upcoming NBC reality show Fashion Star alongside Nicole Richie.