Kim and Khloe check out the cake as big sis Kourtney sips a drink. Family, friends and partygoers sang "Happy Birthday" as Kourtney blew out the candles on her Bombay Sapphire blue cake.
Kourtney's sisters teamed up with Bombay Sapphire to throw her a 31st birthday party at Wet Republic in the MGM Grand in Las Vegas. Though Kourt's actual birthday was April 18, the Vegas festivities took place on April 24.
Click through for more party shots!
(Wire Images/ Denise Truscello)
Kim, 29, Kourtney, 31, and Khloe, 25, show off the Bombay Sapphire birthday cake poolside.
(Wire Images/ Denise Truscello)
The trio hung out with pals and celebrated the new mom’s day in an ultra exclusive Bombay Sapphire bungalow. The group danced to tunes spun by DJ Hollywood.
(Wire Images/ Denise Truscello)
The reality TV sisters enjoyed Bombay Sapphire Rasberry Collins during Kourtney's poolside celebration.
(Wire Images/ Denise Truscello)
The newest Kardashian is already a star!
The eldest sister Kourtney gave birth to Mason Dash Disick earlier this month with boyfriend Scott Disick, 26.
Click through to see more of Mason and the Kardashian clan.
Despite sources saying that Mason's dad Scott is bad news, the couple seems happier than ever in the Life and Style spread, telling the magazine that it feels "amazing" and "indescribable" to be parents.
Disick said. "My first time holding him was definitely special. But holding him the second time was even more special, and the third time was even more special than that. I fall so much more in love with this kid every day."
<a href="http://www.lifeandstylemag.com/">Click here to read more from Life & Style.</a>
The reality star sisters stripped to their skivvies to promote 'Keeping Up with the Kardashians' season four... even pregnant Kourtney!
Kourtney is due to give birth around Christmas, but she wasn't about to skip out of the risque lingerie shoot. Black undergarments highlight Kim's booty, Khloe's long legs, and Kourtney's baby bump (are those sexy now?).
The racy promo poster promotes season four of the series, premiering December 13 on E!
Click through to see the poster in its entirety, and a better look at each sister.
Teasing "what a difference a year makes," the poster references the changes the girls have gone through last season, notably Khloe's quickie September wedding to L.A. Lakers star Lamar Odom and Kourtney's surprise pregnancy.
Kourtney highlights her baby bump with black lace. The eldest Kardashian sister, 30, is due to give birth to a baby boy on December 23. On-again-off-again boyfriend Scott Disick is the father.
Now Mrs. Odom, the 25 year-old will look for a new home with her husband Lamar this season.
Kim flaunts her famous rear in the promo poster.
The original famous Kardashian sister, 29, will face a stalker this season. Yikes!
Feb. 2009: Sisters Khloe and Kourtney Kardashian party without sister Kim. (AP)
Stepping out without Khloe, the Kardashian sisters hang out in Park City, Utah during the Sundance film festival. L to r: Kim, brother Robert's ex-girlfriend Adrienne Bailon and Kourtney Kardashian. (AP)
Khloe Kardashian strikes a pose on the red carpet. (AP)
Dec. 31, 2008: The Kardashian sisters, (l to r) Khloe, Kim and Kourtney ring in the new year in Las Vegas. (AP)
Dec. 2008: Kourtney and Kim Kardashian work the red carpet. (AP)
Feb. 2009: The Kardashian women with pet chimp "Suzy." (AP)
Feb. 2009: The Kardashian sisters, (l to r) Kourtney, Khloe and Kim at a press event. (AP)
Kim shows off her domestic side. (AP)
Feb. 2009: Khloe and Kim Kardashian at the Badgley Mischka show at New York Fashion Week. (AP)
Feb. 2009: Khloe and Kim Kardashian at the Badgley Mischka show at New York Fashion Week. (AP)