Kim Kardashian, Robert Kardashian, Kris Jenner

Courtesy of Denise Truscello/WireImage

Rob Kardashian rang in St. Patrick's Day with a big birthday bash!

The Keeping Up With the Kardashians star, who turns 25 today, hit Sin City this weekend to celebrate with big sister Kim Kardashian, mom Kris Jenner and younger sisters Kendall and Kylie Jenner.

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"Let the festivities begin," Kim tweeted Friday, along with a photo of her, Rob, Kylie and Kendall in their hotel room before the shindig.

"Can't wait to see what everyone in #vegas is talking about. @1OAKlv for my birthday celebration tonight!," Rob chimed in early Friday.

While Kendall and Kylie headed back to their hotel suite after dining with their bro at Stack Restaurant & Bar in the Mirage Friday night, Kim and Kris continued the party with the birthday boy at the Las Vegas hotel's 1 OAK Nightclub, where he was treated to a colorful tiered cake created by chef Jean Philippe, sources tell E! News.

And the over-the-top cake was just the beginning.

The trio partied into the night, toasting shots to Rob, with Floyd Mayweather Jr. later joining the festivities.

And although Khloé and Kourtney missed Rob's birthday celebration, they made sure to show their love for their baby bro via Twitter.

"Happy Birthday to my brother @RobKardashian wooohoooooo," Khloé tweeted Saturday.

Kourtney also gave Rob a shout-out, writing "Happy Birthday to my favorite brother @RobKardashian!! Missed you guys last night! I love you so much. Come over for some cinnamon booty!"

Happy 25th birthday, Rob!

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