The couple shared their happy news while attending an event in New York last night alongside Ashlee's six-year-old son Bronx Wentz.
Ashlee looked fabulous in a leather leggings and an oversized dark red shirt which kept her blossoming baby bump away from view.
She told People she'd wanted to know the sex of her unborn child so she could get started on preparations including a nursery.
Ashlee, 30, and Evan, 26, announced the pregnancy in December, just a few months after they married at Evan's mum Diana Ross' estate in Connecticut.
They'd become engaged that January.
Ashlee and Evan took Ashlee's son Bronx to a Crayola Colour Alive event in New York City on Thursday (5 February), where they were pictured joining him in playing with colouring books.
Bronx is Ashlee's son with ex-husband Pete Wentz.
Little Bronx is already big brother to dad Pete's second son Saint Laszlo, who was born last year. Pete's in a relationship with model Meagan Camper.
Reveal is now on Google Plus! Join us here for the latest pictures, fashion and celebrity news!