The couple - who are already parents to daughter North, four, and son Saint, 23 months - are expecting their third child via a surrogate and the 37-year-old star has now confirmed the gender of their baby, who will be born early next year.
'I think it is so much harder to go through it this way, because you are not really in control, ' she admitted.
Ellen picked up on what she said and replied: "She's a toy tester. and you just told us it's a girl".
"'My daughter thinks she's tricky".
Once the cat was out of the bag, Kim continued, saying, "North is really excited about that".
Kim Kardashian: 'Surrogacy is a hard experience'
If you're curious as to the name of the child, you're gonna have to live with it for a little while as the only name she's been identified with so far is "Baby Sister" Kim, however, says she's open to suggestions.
"People brought toys and gifts, and [North] was opening them all up the next day", she said.
She explained: "It's been such a fun journey to figure out how our kids like to dress and how to make cool clothes for kids". But Kim is still struggling with a name for her baby. Apparently, North West is getting into the toy testing business.
"And then she did makeup on the My Little Pony that they gave and she said, 'Mom, I want to do a YouTube video". "She names everything Star West".
"I said, 'What do you wanna name it?' and she said 'Star".
Kylie Jenner and Khloe Kardashian's rumoured pregnancies have been dominating headlines since news of them broke back in September.