@FanOfMostEverything  
Oh good, for one second, I thought this was “Celestia has a secret, SHE’S EVOL” bullcrap. Glad to know it’s just mildly contrived yet somewhat interesting fanfiction.

From the source:
 
This piece revolves a round a room holding a dark secret that Celestia has hidden from the rest of her subjects. The Secret is Twilight’s origin. (FAN-CANON AHOY!) During the terrible battle between Celestia and Nightmare Moon, Celestia clearly had the upper hand due to the Elements of Harmony being in her possession. Nightmare Moon knew she was finished, and fearing an abrupt end channeled her dark energies to create an offspring to take up her quest for revenge against those who spurned her night. Nightmare Moon did not however die, Celestia still loved her sister, even if Luna had descended into madness caused from Jealousy. The Elements sensed this, and instead of destroying Nightmare Moon imprisoned her. Nightmare Moon was still in the process of finishing her child, the elements purified her offspring and instead of a new evil being born a small little alicorn was created. Celestia being wise saw this as an opportunity she could not pass up took the child and stasis froze through a crystal hibernation. Twilight was awoken by her aunt at the right time and given to a family to be raised as a normal foal. Twilight powers were restrained and monitored. Celestia took care and guided everything just so all the pieces would be in place to save her sister. Twilight did save her mother, and even reclaimed her godhood later. The problem is WHAT is twilight is she really a child of Luna or is she just a part of Luna’s soul, that will have to rejoin with the Mother? Celestia having massive guilt for all this and Luna with no recollection of these events, Pushed Celestia to keep the farce up. But the room was discovered secrets revealed.