Phosphoros ed Hesperus

They ... no, she wasn't always like that.
Everyone knew them as the Evening Star and her sister, the Morning Star, both were bearers of lights.
Both symbolized the light of day and night, however the day was always brighter than the night and one sister became jealous of the other.
Unfortunately jealousy led to tragedy.
The Evening Star stole her sister's light by tearing off her golden wings and while one passed away in the dark the other one shone with a new light.

The two sisters no longer exist, now they are one entity and for better or for worse, in the light and in the dark they will remain together... forever.