Kourtney Kardashian welcomed her third child with boyfriend Scott Disick on Sunday, Dec. 14. Credit: Paul Zimmerman/Getty Images

Her own little clan! Kourtney Kardashian welcomed her third child on Sunday, Dec. 14, a baby boy, sources tell Us Weekly. It also happened to be her son Mason Disick's fifth birthday.

The reality star, who is already mom to Mason, 5, and Penelope, 2, with longtime love Scott Disick, couldn't be more ecstatic with her growing brood.

Prior to going into labor, Kardashian shared a picture of a baby doll lying in her newest addition's crib on Instagram on Dec. 13, captioning the image, "Nap time! Someone's already using our new crib."

Nap time! Someone's already using our new crib.

A photo posted by Kourtney Kardashian (@kourtneykardash) on Dec 12, 2014 at 6:33pm PST

While nine months pregnant with her second son, the eldest Kardashian sister posed nude for DuJour magazine and gushed she feels her best while pregnant.

"I had done a nude shoot when I was pregnant with Mason, really last minute just for myself, and I love it," she told DuJour of why she decided to drop trou. "This time, we were shooting for our show, and everyone on our camera crew was like, 'You are so comfortable just walking around naked and pregnant!' [But] what appeals to me is celebrating the shape of my body being pregnant and capturing that time in my life...It's a wonderful thing to be able to show my children these photographs one day and say, 'This was you inside'…I'm at my best when I'm pregnant.," she added. "It's such an amazing feeling, the transformation that your body goes through. There's something about that that's so empowering and beautiful."

Us Weekly was first to break the news the 35-year-old mom was expecting again this past June. Kardashian confirmed she was expecting herself when she surprised Disick with the news during the premiere episode of Kourtney & Khloe Take the Hamptons.