Image imported from derpibooru 
Original Description:
 
Canterlot audience that includes Princesses Celestia and Luna.
 
The power-mad prestidigitator has apparently mastered a spell that causes her to swell and float into the air. Most of the audience is stunned by the spectacle, unsure of whether they’re witnessing some cleverly crafted inflatable fashion, or mystically expanding flesh beneath. The two celebrity spectators in the front row are reacting differently however. Luna appears more interested in the deep blush and panicked silence afflicting her sister.
 
Celestia, who created this very spell for herself and kept it secret for hundreds of years, is torn between abject fear and imperturbable arousal. This power-mad minx is flaunting her most secret, carnal ritual right in front of her, her sister, AND thousands of their subjects. After all, Trixie is a practical stage entertainer who doesn’t know any REAL magic! It’s not like she could work a spell designed by a goddess, even if she happened to randomly DREAM it up one day.
 
If only Celestia weren’t so mortified that she failed to notice her sister’s barely-contained glee. Until she catches on and goes full-ham on Luna, you can see the ritual in action by following the link below. (It’s a 7-page adult comic starring Celestia and her fungeon)
 
https://www.weasyl.com/~krafty/submissions/1009278/celestial-eclipse-1-of-7