Justin Bieber & Kylie Jenner Snap Instagram Picture in Las Vegas

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It's one of the ultimate disses when your boyfriend (on-again/off-again in this case) and your "best friend" hook up; what makes it even worse is when they throw their new relationship in your face. And that's exactly what appears to be happening to Selena Gomez as sometimes boyfriend Justin Bieber went out with short-term bestie Kylie Jenner. There's Instagram proof!

After Selena unfollowed the youngest of the Kardashian/Jenner clan on the social media site (then everyone, including JB, eventually), Justin returned the favor by deleting his ex from Instagram as well. Now, the war continues as he snapped a picture with KJ — in Sin City!

Instagram (@justinbieber)

After the Floyd Mayweather fight, the Biebs posted the above photo. The caption didn't give away any real information, but it still made fans scream with all the WTFs. What do you think is going on between Kylie and Justin? Tell us your thoughts on the sitch in the comments!

Learn more about Justin Bieber's new track, "Sir Bizzle," here:

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