Khloe Kardashian “Counting Down” Until Kourtney Welcomes Baby Number 2

 Jason LaVeris/FilmMagic

Khloe Kardashian is an antsy aunt!

On Wednesday afternoon, the reality star, 27, happily blogged about sister Kourtney's second pregnancy — which she announced first to Us Weekly in an exclusive new cover story.

"I am BEYOND thrilled to fiiiiinally be able to share with all of you the fabulous news that my beautiful big sister Kourtney is expecting yet again," Khloe wrote beneath a snapshot of Us Weekly's newest cover featuring Kourtney, 32. "Can you believe it?! Masey is going to be a big brother! We are all so overjoyed by this wonderful news and are counting down the minutes until we get to meet the newest member of our family."

The baby-to-be is the second for Kourtney and Scott Disick, her beau of 5 years; their adorable son Mason turns 2 later this month.

The Kim and Kourtney Take New York starlet tells the new issue of Us that she's about 9 weeks along.

Added proud sister Khloe: "Kourtney is the greatest mom in the world and I am so proud of the woman she has become. I can't wait to see her with a kid in each arm! She'll be a pro. LOL."

For much more from Kourtney and Scott on their baby joy, pick up the new Us Weekly, on stands Friday!

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