Kim Kardashian's Bum Threatened By Jen Selter's Pert Rear

Just when you thought bums couldn't get any bigger, an Instagram star steps up and takes on the challenge of everyone's favourite reality TV bottom.

Yes, for some people Kim Kardashian's kurvy behind will always be the one bum to rule them all, but hot on her heels is pert-bottomed selfie-taker Jen Selter, whose glutes have got Instagram all fired up.

Only yesterday, Kim's famous derriere found itself splashed all over the internet as it posed teasingly on the edge of a boat in Thailand.

But Kim should be wary of sitting too comfortably, because if there's one bum we want to stare at all day, it's probably Jen's.

Squat lover and all round fitness champion Selter has made a name for herself as the best bum on Instagram, posting snaps of herself - and her perfectly pert cheeks - in a variety of gravity-defying snaps.

The 20-year-old, from New York City, has had so much attention for her round behind, not to mention the millions of followers she has on Instagram, that she says she can't even visit public gyms anymore.

Well she says that, but judging from her snaps she's quite happy to work out her fabulous bum in any number of public places around New York.

From Central Park...

...to the subway

But that's beside the point.

Jen wants to keep the focus on her best asset: "I'm recognised wherever I am. I don't really go to public gyms anymore just because it is a whole big scene when I'm there. I don't like being watched.

"I don't really post a lot of face pictures..." she added. "They don't want to see my face."

We're sure some of her nearly-3,000,000 followers are just as keen on her face as her butt, but we've got to admit, it's pretty mesmerising.

And unlike Kim's it seems acheiveable, with an astronomical daily quota of squats.

To the gym, ladies!