In his announcement, Ferguson said that he would be out for two shows, returning to the stage for the Thursday night production. "My incredible understudy @timothytwright will be on tonight and tomorrow," he wrote. "I know Tim has you all in wonderful hands."
Sarah Hyland was among those commenting their congratulations to the new parents, writing, "The SWEETEST." The couple also got "congratulations" from Vanessa Williams and Sophia Bush, among many others.
Uzo Aduba shared her excitement, writing, "Awww. Congratulations to all and welcome, baby Sullivan!!" Amanda Seyfried commented, "Jesus what a day! Congratulations sweet boys!!!!"
Over on his Instagram Stories, Ferguson offered fans a sneak peek at Sullivan's nursery, all ready for the little one to be spoiled by his doting fathers and big brother when he gets to come home.
You can check out all the adorable decorations, including his little stuffed sloth, below.