"How could you not look at her? She looks gorgeous!" Hammer gushed to ET's Lauren Zima.
The 30-year-old Birth of a Nation star added that any nerves about their expanding family are quickly subsiding.
"I'm a little less nervous. You have a little more faith in the human mechanism," he said. "The only reason you're here and I'm here is because it works. We got through with one good baby, I think we can do it again."
The couple already have a daughter, Harper, who will turn two in December, and Hammer is equally excited to have a baby boy on the way.
"It's one of those things where if I am dreaming, I don't want anyone to pinch me," he said regarding his budding career and growing family.
Following the premiere, Hammer and Chambers finished the night at home with a couple of double In-N-Out burgers. "About last night… #doubledoublesanddoubleD's," the proud dad captioned the happy photo.
Nocturnal Animals opens Nov. 18. For more on the Tom Ford thriller, watch the clip below.