While Jenna is already mother to six-year-old daughter Everly with ex-husband Channing Tatum, the baby will be Steve's first, and he opened up about his other half's pregnancy journey during an interview with Entertainment Tonight.
"It's mind-blowing, the whole thing," he gushed. "Watching a child grow inside of a human has been the most amazing experience so far. It's good! I'm trying to stay calm and not panic and let it all happen."
Actor Steve is planning to take a year off of work so he can be there for Jenna and their baby.
Explaining his reasons for doing so, the screen star said: "I just want to see all this process. This is my first child, so I just want to be there for Jenna, for the whole thing and that's going to be it. My next role is just dad and that's it!"
"I don't want to miss any doctor's appointments. I don't want to miss any of the baby growing. I don't want to miss any of the morning sickness. I want to be there for all of it."
As for how Everly's feeling about becoming a big sister, Steve insisted "she's excited!", adding: "She couldn't be happier. She's very excited to have a sibling on the way. It's going to be good."