A few years have passed since Princess Luna was purged of the evil known as Nightmare Moon by the Elements of Harmony. She took back her rightful place on the throne of Equestria at her sisters side.
On a sunny day, a couple of seemingly mundane events trigger memories long forgotten. Memories of a secret Luna hast kept to herself for far too long. Facing Celestia won't be easy. But she has no choice. It is her duty to care for her subjects, and she has to retake the responsibility she could not fulfill while banished to the moon.

In terms of full disclosure, the story got a review by TheifofZ.

What has happened since her disappearance? What will she find? A joyful reunion or devastation? What happened to her Children of the Night?

Inspired by Children of the Night. Cover art is a screenshot from the video. I do not know if there is an "official" story for the Children of the Night and I do not claim mine to be "canon" in the context of the video. These are just my thoughts on what might have happened back in the days.

This story takes place right before the season 4 finale.