After checking this piece against other WhiteDiamonds work, I’m convinced it’s not hers. However, it is a VERY good aping of her art style.
 
The differences are subtle, but they’re there. WD’s lines are cleaner & thinner than this, even in her quick-sketches. Her shading is blended better. She draws their eye-shinies larger than this and with more of the iris colour. Finally, WD doesn’t draw Rarity’s horn twisting like that. However, I’m not going to change the artist tag. Shame it wasn’t signed.

Oh wow, this is beautiful!

It looks like WhiteDiamonds to me

Doesn’t quite look like WD and plus she always puts her signature on the bottom right corner of her work.

It was certain it was WhiteDiamonds from the thumbnail, but looking at the full size one I’m not so sure.

I second the source request!

seriously who’s the artist?? I almost thought of WhiteDiamonds, not because its RariJack

 
Omg who drew this?!

Now who drew this?

“you filthy little filly”