The 35-year-old reality star revealed as much in an interview with People this week. Kardashian and longtime partner Scott Disick are parents to 5-year-old son Mason and 2-year-old daughter Penelope, and welcomed Reign in December 2014.
"I'm never certain [with names] until they're born, [but] I love it!" she said of the unique choice. "I actually had the name on our list with Mason. Then, with Penelope, I had it on the list but spelled R-A-I-N ... Once I found out I was having a boy, we just changed the spelling again."
Kardashian and Disick have been in an on-and-off relationship since 2006, and welcomed Mason in December 2009. Penelope followed in July 2012, and the reality star took to Instagram to share a new photo of her daughter Tuesday.
Kardashian posted the first full-body picture of Reign on the photo sharing site in early April. The reality star and her family recently returned for a 10th season of E! series "Keeping Up with the Kardashians," which airs Sundays at 9 p.m. ET.
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