Kendall Jenner is closing in fast on becoming the women with the best behind in the Kardashian household after she photobombed Kim's gym pic.

On Friday the reality TV stars hit the gym together in matching tight gym pants and crotch tops.

As usual Kim wanted to let all her followers, on social media, know that she was working up a sweat.

However, unlike the usual gym selfies, her little sister decided to get in on the act and jump into the photo as it was been taken.

The caption read, "Barging in on Kim's booty self." It must run in the family because the 18 year-old showed off her equally amazing behind, if not better.

The new selfie comes after Kim's last post-workout gym photo caused a stir on the internet.

Earlier this week, Kim caused controversy when she posted a similar photo with her friend and workout partner, Blac Chyna.

The 33 year-old flaunts her famous curves and tight gym attire, but the pic has garnered attention for the wrong reasons, she has been accused of photoshopping herself to exaggerate those famous curves for the camera.

Well, the future wife to Kanye West was clearly angered by the negative response and took to twitter to set the record straight.

"It sucks when people make up surgery or Photoshop lies," she tweeted, "when I am so disciplined & work so hard! Just trying to motivate others & show anyone struggling with weight they can totally achieve whatever they want if they are dedicated!"

Kim gave birth to baby daughter North West, in June 2013 and has already managed to lose most of her pregnancy weight and achieve the figure that she is famous for.

Which booty is the best?