11/30/2011 AT 06:30 PM EST
The warm wishes continue to roll in for Kourtney Kardashian
, following the announcement Wednesday morning that she and longtime beau Scott Disick are expecting their second child
"Masey is going to be a big brother!" an "overjoyed" Khloé Kardashian
, 27, wrote
on her blog. "We are counting down the minutes until we get to meet the newest member of our family."
Praising her older sister, 32, as "the greatest mom in the world," Khloé raves that she is "so proud of the woman [Kourtney] has become."
"I can’t wait to see her with a kid in each arm!" Khloé goes on to say of the mommy of son Mason Dash Disick
, who turns two next month. "She’ll be a pro. LOL. And if this next baby is anything like Mason, then we will truly be the luckiest family in the world."
Sister Kim Kardashian
couldn't contain her joy either.
"It's sooo exciting!" she told PEOPLE earlier in the day about the news. "They are so happy and so am I!"
Additional reporting by JENNIFER GARCIA