The 24-year-old actress/singer, who is four months into the pregnancy, is excited about the couple's first child.
Duff told the Ellen DeGeneres show in an interview set to air Monday that she just learned it is a boy, but had a feeling it was all along.
Duff told Ellen DeGeneres, "I haven't told anyone yet. I wanted to tell you first. I just found out. It's a boy! I had a feeling it was a boy the whole time."
Comrie, 31, who played 589 games during his NHL career, played for the Pittsburgh Penguins last season, scoring one goal and dishing out five assists in 21 games last season.
Duff is pleased with how her pregnancy has progressed thus far. "I feel great, actually. It's been super-easy."