Princess Nightmare Moon had tried to keep it secret. She had feigned ignorance, but the charade could not last. She nocked the arrow. Tirek was a large target; he would fall easily. Then the true challenge would come: explaining herself to Celestia.
She looked just like Princess Celestia, except marred and broken. Her ceremonial barding had rusted slightly. Black streaks ran through her mane. Worst was the scar across her chest. The tarnished Celestia smiled at Luna. "H-hello, monster."
Luna reread the graffiti, but it came no closer to making sense. “Princest Is Wincest,” it said. It was confusing enough to be offensive; did nopony spell correctly anymore? Perhaps Tia would be able to explain it.
Nightmare Moon won. She defeated Celestia, broke the Elements, banished the sun. This all happened a very long time ago. So long ago, that she has had plenty of time to change her mind. Not that fixing it will be simple.