Kourtney Kardashian Posts Sweet Birthday Message to Her Boys Mason and Reign

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Here's to the birthday boys!

Kourtney Kardashian's boys, 6-year-old Mason and 1-year-old Reign share a birthday, and the proud mama shared a sweet pic of the brothers on Monday, writing, "Happy Birthday to my sweet boys who forever changed my heart! I still can't believe they have the same birthday."

WATCH: Kourtney Kardashian and Justin Bieber Aren't Hooking Up, Source Says: 'She Wouldn't Go There'

Kourtney -- who also has a 3-year-old daughter Penelope with her ex, Scott Disick -- treated her boys to alien laser tag over the weekend, which was well-documented on the family's social media accounts.

PHOTOS: Stars Share Pics of Their Cute Kids

Kylie Jenner posted a photo with Reign, and Kendall, writing, "the cool aunts."

the cool aunts 😎

A post shared by Kylie (@kyliejenner) on

Meanwhile, the rumor mill was swirling this weekend that Kourtney and family friend Justin Bieber were reportedly in a May-December romance! However, a source told ET on Monday that it is simply not true.

"Kourtney wouldn't go there," the source said, saying the two are just "good friends."

WATCH: Kourtney Kardashian Celebrates Sons' Birthdays With Alien Laser Tag Amid Justin Bieber Rumors

Watch the video below.