Image imported from derpibooru 
Original Description:
 
For Twilight’s coronation Rarity has worked tirelessly with assistants Coco and Sassy to make a dress fit for a princess. Twilight tried multiple times to tell Rarity that she should go through all this effort but Rarity insisted. At the final fitting just days before the coronation Rarity gets Twilight to try on the dress proper.
 
It fits perfectly a dress truely fit for royalty, but not for long. Suddenly the dress starts to be eaten away by the excess magic produced by Twilights body. It’s. It long before enough of the dress is eaten away that her breasts have the strength to break free causing the pendant on the dress to go flying hitting poor Sassy. Poor Rarity all that work destroyed in an instant, if she’d listened to Twilight she would have know this would happen, there is a reason why she goes around naked.