updated 11/30/2011 AT 12:00 PM ET
•originally published 11/30/2011 AT 6:00 AM ET
“It’s soooo exciting!” her sister Kim tells PEOPLE. “They are so happy and so am I!”
Kourtney, 32, and Disick, 28, who have been together for four years – on a sometimes rocky road involving their relationship – will also soon be celebrating son Mason Dash Disick’s birthday. He turns 2 on Dec. 14.
Soon after Mason’s arrival, Kourtney’s younger sister, Khloé Kardashian, even remarked on what a change he brought to her sibling, Tweeting: “Wow my sister has changed. She used to whip her boobs out for no reason. Now she does it to feed her child.”