The fateful day, that dear sweet Fluttershy visited the crystal empire, a visit meant to be short due to the terrible conditions, was the day her otherwise normal and peaceful life changed forever, as something most unexpected happened. The former tyrant, king Sombra broke free from his icy confinement and was ready to claim the empire once again, and with no princesses to stop him, he was victorious. In the aftermath of his takeover, ponies where once again slaves, forced to care to the king's every cruel need. Fluttershy, with no way to return back home, was promptly forced to become a prisoner… not like she was going to stand up anyways. It didn't take a long time for sombra to notice the black sheep of the herd, or rather the yellow Pegasus amongst the shiny crystal ponies… and golly was she a beauty. The dark stallion was oddly infatuated with this meek mare, and didn't know what to do… until he realized that he is a dumbass and could just take her, since you know… evil overlord. I am pretty sure that you can guess what happened next so no need to explain any freaky details…
Alas, prince alastor was the result of this cursed union. In the first few years of his life, he was raised by Fluttershy and built a strong bond with her since at the time she was the only pony in his life. That was at least until his father started training him and feeling his young mind with beautiful words of power, domination and perhaps a little bit of evil. Alastor completely adored his father and really wants to him proud of him by being cruel and cold to others but there are moments of weakness where he forgets that he actually isn't supposed to help the prisoners. He still sees Fluttershy sometimes but since he has changed so much, they end being awkward with each other, their meetings ending in him either yelling at her or straight up giving her the cold shoulder.
Alastor is a very talented and strong magic user, sometimes able to come up against Sombra. He guards the borders of the empire and eliminates anyone who he deems a threat… and anyone I mean everyone. Since the crystal empire and the rest of equestria are now at war with each other, he has to be extra careful and observant of the ins and outs of his home. And what would you know, one of the princesses of the new and weird royal family is constantly trying to break in and gather info. Alastor and the princess, which he later learned her name, Cassandra (he would say her name was beautiful if he didn't "hate" her so much) constantly engage in duels, while simultaneously shit talking each other. A third party would even say that these wannabe fights are friendly, if not downright flirtatious, but the dark prince and the draconequus princess would claim that there is noting but a sheer hatred between them….