The Royal Sisters Arc 3 (Part 3) END

Nightmare Moon's existence disappeared like smoke, and the magic that ensnared Celestia was also broken. All that was left were two sisters.

It was the first time in a very long time that Celestia saw a familiar face. A face she feared that she would forget.

Pseudo-Immortality prolongs aging, but it doesn't increase your memory capacity. Celestia had to deal with the slow process of her memories fading. Even now, Celestia could barely remember the faces of her parents or the pain and anger she used to feel as she grew up with Luna, it all seemed so trivial and unimportant now. 

She changed, she was older and wiser than when she was a teenager. With something like Pseudo-Immortality, the ideas of prolonging negative emotions would only drain you. And so Celestia decided to let it all go. 

Luna was and will always be someone in the same boat as her. Rather than push her away, she embraced her long lost sister.

Luna understood quickly that her sister wasn't angry, and a wave of relief washed over her. When the tired-ness set in, all Luna could do was cry in her sister's arms.

In the face of the six ponies that freed her little sister Celestia introduced a new reign for Equestria. Two sisters ruling side by side. As it should have always been.