"I think I was most excited and allured by the fact that John would be the best father to a little girl. That excited me," she continues. "It excited me to see … just the thought of seeing him with a little girl. I think he deserves a little girl. I think he deserves that bond."
The 30-year-old supermodel says the couple will eventually have a son too.
"A boy will come along," she says. "We'll get there too, so it’s not like we really have to pick. But he definitely is very lucky to have a little girl. And this girl is going to be so completely lucky to have John as her papa -- it's crazy!"
"A couple minutes after this shot, John and I learned we were having our little baby girl!" she wrote.
Legend, 37, also shared the same photo to Instagram, gushing over his wife's cover pic that was shot "the day we found out we were pregnant with our baby girl."
When ET caught up with the couple at the GRAMMYs earlier this month, Teigen said they were "working on" writing a new song for when they welcome their first child this spring.
"We need to figure out her attitude first," the cooking aficionado told ET exclusively. "She might be a nightmare. We don't know. Everyone just assumes she'll be the sweetest thing on the planet [but] she might be a little hard."
And they have yet to decide on a name!
"We have maybe 10 options we just switch through," Teigen shared. "We can't pick. We've got to see her."