The reality star's sister Kourtney Kardashian welcomed a baby girl with long-time boyfriend Scott Disick on Sunday (July 8). The couple already have a son, Mason, together.
"I'm an auntie again!!!!!!!!!!," Khloe wrote on her blog. "As I'm sure you all know, my beautiful big sister gave birth yesterday to the most perfect baby girl you've EVER seen - Penelope Scotland Disick!"
"The entire family is literally exploding with joy and have not stopped fawning over our new little girl," she continued. "And Mason is already loving being a big brother! This is just such a special and happy time for my family. Thank you to Kourt and Scott for making such beautiful babies! LOL."
On Sunday, Kim Kardashian also took to her blog to congratulate her sister on the birth.
Khloe has been named as a contender to host The X Factor USA.