Twilight Sparkle went to the Canterlot Castle one day to discuss things with Princess Celestia. Only when she opened the door she found the sun princess on the floor lifeless, she had taken her life with a forbidden spell, leaving only a husk of the formal ruler. Something was unhinged in the purple alicorn that day, she was locked away by Princess Luna to prevent any harm to her or others. She showed signs of psychosis and was given a ring to halt her magic. Twilight was found a few days later with her horn practically shattered from her constant banging her head against the wall. Recovery is not expected. 

Friendship is Dead// thehappiestgolucky TeVeeHead and I