The 41-year-old Broadway star revealed the happy news during an appearance at Sirius Radio Studios on Monday (August 4).
“Breaking news!!! @StephanieJBlock 4 months to go til #BabySebOrSteph,” Sirius/XM Satellite Radio’s On Broadway host Seth Rudetsky shared on Twitter.
Their future baby will be a new addition to the family, which also includes their pet pooch Macaco.
Sebastian and Stephanie, who both starred together in Broadway hit show Wicked, tied the knot in October 2007.
Congrats to the couple on the happy news!