Update

Kourtney Kardashian Is Pregnant

UPDATED 11/30/2011 at 12:00 PM EST • Originally published 11/30/2011 at 06:00 AM EST

And baby makes four: Kourtney Kardashian and longtime love Scott Disick are expecting their second child.

"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.

As the Kourtney & Kim Take New York star told PEOPLE during her first pregnancy, "This baby was unexpected, but it's 100 percent a blessing."

PHOTOS: Who's Due Next?

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."