For Kourtney Kardashian, deciding on a name for her third child wasn't easy.

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Not only did the Keeping Up With The Kardashians star have a number of names to choose from, she also waited until the last minute to make things official.

“I’m never certain [with names] until they’re born,” Kardashian explained to PEOPLE Magazine on Monday. However, once she decided on Reign Aston, she knew she had made the right choice. "I love it!"

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“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,” Kardashian continued.

Along with partner Scott Disick, Kardashian has three children, Mason Dash Disick, 5, Penelope Scotland, 2, and Reign Aston, 4 months.

Because Kardashian believed her third child would be a “girl in the beginning,” she was leaning towards naming her Rain. However, once she and Disick discovered they were having a boy, she changed the spelling.

Following Reign Aston's birth, Kardashian returned her focus to the Kardashian Kids collection, which launched yesterday on Nordstrom.com.

“We put so much into it and were constantly sending references to each other,” Kardashian said of herself and her sisters, Kim and Khloe. “We take a lot of pride in the line and we’re all kind of perfectionists and very detailed oriented."

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