Looking for a story where Celestia and Luna move on, and transfer control of the Sun and the Moon (as well as Equestria) to Cadence and Twilight.

I remember reading it, but can’t remember the name. Any suggestions?

Shit! I actually remember reading a few fic's like this but I can't remember any of there names.

4757007

http://www.fimfiction.net/story/116254/princess-twilight-sparkles-500th-birthday

Is this it?

There's a few stories with this mind, though the ones I know are one-shots.
First are these two linked stories; Mournful Sunsets and A Lost Moon.
Second is this; Departure.