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​Kourtney Kardashian celebrates sons' birthdays with alien laser tag amid Justin Bieber rumors

Kourtney Kardashian definitely knows how to party.

The 36-year-old "Keeping Up with the Kardashians" star celebrated the upcoming birthdays of her two sons, Mason Disick and Reign Disick, on Saturday, as rumors around her and longtime family friend, Justin Bieber, continue to swirl.

The alien-themed outdoor birthday bash -- complete with a screening of "Home," a bounce house and laser tag -- took place at Khloe Kardashian's house, and from what we've seen on their family's social media posts, it looks like things got a little weird.

"Alien laser tag," Kourtney captioned a group photo from the night, followed by with a close-up shot of some of the decorations.

Kourtney's youngest child, Reign Disick, turns one on Dec. 14 and made appearances in posts from two of his aunts, Kendall and Kylie Jenner. Reign shares his birthday with his older brother Mason, who will be turning 5.

"Me as a mom," Kendall jokingly captioned her photo, which was re-grammed by her mom, Kris Jenner.

Kylie's post featured Reign in gif-form. "The cool aunts," she wrote.

A source told ET that Kim Kardashian and her newborn, Saint West, were absent from the party, but her husband, Kanye West, and 2-year-old daughter, North West, were both in attendance, along with Kourtney's on-again, off-again boyfriend and father of her three children, Scott Disick. Kourtney and Scott are also parents to 3-year-old daughter, Penelope Disick.

Earlier this week, Kourtney partied with Justin in West Hollywood, California. A source told ET that the two were "nearly inseparable" on Friday night, as they were spotted together inside The Nice Guy. Justin gave an impromptu performance on the piano at the swanky celebrity hot spot, which seems to be a favorite for both Justin and Kourtney, as they were also spotted there together in October.

Their recent outings together have sparked romance rumors, including reports that the two are hooking up and that Justin is reportedly bragging about it to his friends. Kourtney and Justin have yet to comment.