On Sunday, December 21, Kourtney Kardashian took to Instagram to share the first photo of her newborn baby boy, E! News reports.

The eldest Kardashian sister also revealed her newborn's name on Instagram, which we now know is Reign Aston Disick.

In the photo, we see Reign's hand holding what appears to be Kardashian's hand in a sentimental moment.

Check out Kardashian's Instagram photo below.

 Madly in love with my little Reign Aston Disick.

A photo posted by Kourtney Kardashian (@kourtneykardash) on Dec 12, 2014 at 8:36am PST

E! News reports that Kardashian and her longtime beau Scott Disick welcomed Reign into the world a week ago on Dec. 14. Reign's birthday coincidentally fell on the fifth birthday of the couple's first son, Mason.

In addition to Mason and Reign, Kardashian and Disick also have a 2-year-old daughter together named Penelope.

Prior to giving birth to Reign, Kardashian opted to pose nude for Du Jour magazine and embrace her pregnant figure.

When asked why she chose to pose nude for DuJour, Kardashian replied, "I had done a nude shoot when I was pregnant with Mason, really last minute just for myself, and I love it. The photo is hanging in the entry of my mom's house."

She added that she feels comfortable posing nude while pregnant because she is at her "best" when she is pregnant.

"To me, nudity is not something to be ashamed of. I'm not embarrassed of my body," she continued. "I'm at my best when I'm pregnant. It's such an amazing feeling, the transformation that your body goes through. There's something about that that's so empowering and beautiful and I just really embrace it."

In a recent episode of "Kourtney & Khloe Take the Hamptons," Kardashian revealed the sex of her third child to her family with the help of her eldest son, Mason, E! News reports.

"Mason ran in here with the blue stick," Kardashian explained during the episode. "There was a red star or a blue star."

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