During Sunday night's premiere of the couple's reality show Rob & Chyna on E!, Chyna had a doctor's appointment in which Kardashian sat beside her and observed his future wife getting an ultrasound.
"That's a nice, normal heartbeat," the doctor told Chyna. "It's regular and there's no problems with the beat of the baby's heart."
The doctor then asked the couple whether they'd like to find out the baby's sex at that exact moment.
"Let's do it right now!" Chyna said gleefully.
"I'm pretty nervous. I'm excited," Kardashian was shown saying in a confessional. "I really want a boy."
The doctor then announced, "You are having -- a girl!"
"Rob, it's a girl!" Chyna exclaimed excitedly.
"Oh, that's crazy," Kardashian noted.
Chyna is already mom to a three-year-old son King Cairo with her ex Tyga, who is Kylie Jenner's current boyfriend, so Kardashian admitted he was hoping for a son of his own.
"It's an emotional moment. Me wanting to have a boy, it definitely stems from my dad, but I'm sure I'll have the same relationship that I had with my father with my daughter," Kardashian told the cameras. "I'm just happy that the baby's healthy and I'm gonna be super happy with a girl."
The doctor joked the baby is "putting her little booty" up, to which Kardashian replied, "She better not be doing that!"
Fans will certainly be waiting to learn the baby girl's name and whether the reality TV stars will continue on with the "K" tradition in Kardashian's family.
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Kardashian, 29, and Chyna, 28, began dating in January, got engaged in April and then announced in May they are expecting a baby together. Rob & Chyna documents the couple's whirlwind relationship as Kardashian and Chyna navigate life together.