The 32-year-old was promoting the new season of her popular reality competition show “Fashion Star.”
Simpson told Ellen she and fiancé’ football star Eric Johnson are “happy” about their little bundle, but were "definitely extremely shocked" when they learned the news.
The fashion mogul – who gave birth to her daughter Maxwell Drew last year - revealed her pregnancy has been taxing this time around.
"This pregnancy is the complete opposite. Like, with Maxwell, I felt amazing. Like, I could do everything, eat everything. Do whatever I wanted. I had a lot of energy. This time around...I'm like exhausted. Eating Tums. That's my snack of choice."
"The first pregnancy, I like, let loose and I kind of ate everything that I wanted to eat and I just really enjoyed it," Simpson added.
"This time around I think because I was doing Weight Watchers and I felt super healthy. I'm not really craving as much and I know how hard it is to get off, so I'm trying to make healthier, wiser decisions."
Simpson and hubby-to-be are expecting a baby boy this summer.