This is the story you have been told. But now the past has returned and wishes to make itself known. As you know, there were once two sisters. One raised the sun, while the other raised the moon. What you don't know is that there was a third. A younger brother. This brother commanded all of the stars.
The brother acted as the balance, the keeper of peace between everything. When a problem would arise, he would be the one to stop it.
You may be wondering as to what happened to the brother. One day, a group of beings, known as the eclipse riders, attempted to kill the three alicorns and take their power for themselves.
The riders had almost won, if it had not been for the brother stepping forth and created a prison from which none would escape.
With the eclipse riders defeated, the three siblings rehoused, but the brother had kept a secret from his sisters.
The riders had attempted to place a curse on the three that would weaken them. When the brother had stopped them, he had knowingly taken the curses. This left him in a great deal of pain, but he refused to let either the ponies or his sisters see his suffering.
One day, the brother chose to leave his place on the throne in order to find everything on his curse, and destroy all of it. With the brother gone, the sisters decide to make equestria safe in hopes there brother would return to them. With each day that passed and no sign of the youngest ruler, the sisters would lose hope. The sisters tried to keep their feelings at bay, but were unable to do so. Sadly, without the younger brother there. A new evil was able to creep its way in and make the ponies believe that the night, and its ruler, were to be feared.
The brother returned and fought off this new evil, but the damage had been done. The younger sister had been lost, and in her place, came a nightmare.
The elder sister used the elements of harmony to seal the nightmare within the moon itself, and took on the roll of raising both the sun and the moon. The brother, set out to find this new evil, and vanquish it.
Now the Nightmare has faded into legend and the brother has been lost to time.
"Hello Nightmare Moon." Swiftly turning to the source of the words, she finds the last pony she wishes to see, and the only one that can free her from her imprisonment.
"What do you want Nebula? I would have thought you were busy playing the anonymous hero. Here to scold me for trying to take what is rightfully mine." The mare in the moon replied with a venomous glare.
"As fun as that would be, no. I have a different reason for my visit." The prince said with little emotion.
"What reason could you possible have to visit your 'banished sister.' I doubt it's anything I would take interest in." This got a raised brow from the male alicorn.
"You're not interested in being freed? Oh well, I guess I'll be on my way." Before Nebula could get any magic working, Nightmare was holding him on the ground. Somehow having a sweet and innocent smile at him. Is she going start growling at me? No, bad thoughts, bad.
"Now Neby, there's no reason for you to leave so soon. Please, stay, and we can talk all about how we're going to overthrow Celestia." There was something about that smile that made the former human remember something from his past life. Is this what it's like for batman when he works with the joker?
"Get off, Nightmare."
"What, I thought you liked it when big sis-" The nightmarish being was interrupted by a swift fist to the jaw, sending her flying away from the know angered immortal.
"You can't fool me, you are not my sister. You are a Nightmare, nothing more. Don't ever try to tell me other wise." The evil being of the night had recovered and changed. With a flex of his magic, his opponent was soon found passed out at his feet. "Now sleep, until the next wielders of harmony come into this world."
Nebula turns and walks away from the sleeping evil that was once his sister. "... And once you're back, I promise to change the stars with you Luna."