I've stood watch over you as you've changed.
And i must say. You've grown to be a fine unicorn. And i am proud of you.
But as you have aged. So have I. And i'm not as young as i was. Not at all.

Princess Celestia has not seen her protige in a very long time indeed. And the time of her and her sisters passing has crept upon her without her realisation. Or anyone else's. Her time has come to a close.
But it is popular opinion that everyone should at least get the chance to make things right before it is too late.