The couple's new bundle of joy will join Simpson's six-year-old son Bronx from her previous marriage to Pete Wentz, reported Ace Showbiz.
Simpson has been showing her support for her husband's newly released music video "How to Live Alone" starring her and her mother-in-law Diana Ross.
"Yay! It's out! I'm excited for everyone to hear my baby @realevanross song #HOWTOLIVEALONE it's so good!!" she tweeted.
Last month at the premiere of "The Hunger Games: Mockingjay, Part 1", Evan hinted at the possibility of expanding his family with his wife.