I write to you not as your Princess but as one pony to another. You deserved a quicker response and I have failed to give it to you in time. You also deserved to have your daughter with you, and I have failed in that as well.
I have no ground to ask for an apology, nor do I deserve it, given the circumstances, but I must express my sorrow to you either way, for it is my fault that this disgrace has fallen Twilight Sparkle.
Perhaps I shall start at the beginning, and keep it straight to the point.
A thousand years ago, I lost my sister due to my own blindness to her feelings. She was morphed by her anger and jealousy into the being known as Nightmare Moon. I managed to subdue her before untold harm downed upon Equestria, but fate saw it fit to punish her with a millennia in the moon.
There was a prophecy made that on the thousandth year, she would return, but I was no longer deemed suitable to wield the magic which banished my sister. And this is where my own hubris came back to cause me pain and rob me of somepony I loved, only this time more ponies have to pay for my conceit.
I saw in Twilight magic unlike I have witnessed in centuries, and in this I also saw hope for the redemption of my sister. It was under my prompting that Twilight studied the tale of Nightmare Moon, assuming she’d take the path I had set for her and lead to the redemption of my sister and a reunion with her after centuries.
But she did not do this.
Instead she chose to hold the full weight of the situation herself, much as I did in the past. And it’s due to her lack of insight on the matter, her limited knowledge of what was truly transpiring, that she now has met a fate much similar to that of my sister.
As you sure have noticed, the moon know has a deep purple shade since the events of the Summer Sun Celebration. Unlike what you may have heard, I played no part in that. The purple shade of the moon is now Twilight’s essence imbued in the same prison as my sister.
I will not ask for your forgiveness, as I do not deserve it. Know that I have my punishment every night when I have to raise the moon and see the remainder of having failed not only my sister, but now also your daughter, and until I find a way to finally atone for my sins, I shall be reminded of it every night. Though now I must also bear the pain of knowing it will serve as a grim reminder of your loss as well.
I cannot ask for your forgiveness, but know that I regret this with every fiber of my being.
Undeservedly yours,
Celestia