Kendall Jenner Kisses Kylie While Celebrating Her 31st Birthday

The Kardashian-Jenner clan is super close ... but Kylie and Kendall have now taken it to new heights ... kissing each other on the lips for Kendall's 31st birthday ... and it's all on video.

That's right ... check out this Instagram video, posted Wednesday, which shows the famous sisters smooching while celebrating Kendall's big day.

As you can see, Kendall asks her sister for a kiss before Kylie makes the move, leaning over and planting a kiss before both start giggling. Interestingly, the video was not posted by either Kylie or Kendall.

Instead, the footage was uploaded by their other sister, Khloe Kardashian, who wrote in the caption, "I love these two little pigeons" and "Happy Birthday to my Kenny, my forever love."

By the way, Kendall's birthday was on Tuesday, when most of the country was wrapped up in the midterms.