Image imported from derpibooru 
Original Description:
 
When Celestia first began teaching Twilight how to raise the sun, it was a joke. The mare had told her that the first time she felt inspired to do something was the day of the Summer Sun Festival. That the princess looked beautiful and amazing she rose into the sky and illuminated the horizon. So of course, Celestia joked ‘You can try it too if you want.’
 
Who knew that since then, Celestia would spend every other morning with her beloved student showing her how to do what she did? As Twilight got better at it, they talked more and would often have breakfast together. Then breakfast became lunch. Then Dinners. It’s unclear who first used the word ‘date’ but she was sure neither of them had a problem calling their get-togethers that.
 
Twilight was the one to make the first move, much to the alicorn’s surprise. Truly, how was she to know their discussion on Timberwolf behavioral patterns would suddenly lead to the mare trying to sneak a kiss? Really, it was only by chance that Celestia’s had turned her head at that moment and their lips met. Neither said anything about it but they shared many kisses afterward.
 
Note: I never really gave much thought to how Twilight and Celestia would become a thing in my universe. All this, [above] I made up as I typed this up. I might keep this though since its cute~