Blaze went ahead and decided to do a colored/alt dialogue version of this  
The story is this:  
celestia was enjoying a nice rimjob by her little sister. She began to use her magic to lightly pushing Luna’s head deeper for her to get her muzzle in there just right, suddenly a loud noise occurred that startled celestia so which made here accidentally push Luna’s head all the way up her royal asshole. (luna’s horn is removed cause it was getting in the way) And now Luna is trying to pull herself out before shit happens