Kardashian, 35, gave birth to the baby on Dec. 14, the same date five years ago on which she and Disick welcomed their oldest son, Mason.
"The family is freaking out with joy," a source told E! News. "What an amazing coincidence."
Kardashian and Disick are also parents to a daughter, Penelope, 2. However, they knew ahead of time that their new addition would be another little boy.
"I am so happy that we're having a boy," she said on an episode of "Kourtney & Khloé Take the Hamptons." "It's going to be perfect for our family."