MLP Future: Prince of Unity

Sky opens his eyes slowly, being blinded slightly by the light of the sun.
"Wait.... Wasn't I inside the cave?"
He looks around, feeling a sense of deja Vu right now.
"I better get back to the school before the graduation ceremony ends." He flies up, looking around to see where he was. What he did not expect was what appeared to be a volcano next to a dark grey castle.
"Um, this isn't Equestria...." He trails off as he sees a silver light strikes the highest spire of the castle, the same color of light that blinded him at the Cave of Harmony! Everything suddenly became a blur, soon resettling in what seemed like a throne room. There were no stain glass windows like in the castle back in Canterlot, but plenty of torches illuminating haunting portraits. The one closest to the throne looked to be damaged, hard to make out who was in it. He slowly flew to end farthest from the throne and found a portrait of an alicorn that looked almost like King Sombra, former king and tyrant of the Crystal Empire. His wings had red highlights in their feathers, and his mane and tail had a similar pattern. His alicorn horn was what drew Sky's attention right away, though. Unlike being the usual spear shape, this alicorn's horn was in a zigzag kind of shape.
"I don't understand. Is it really possible for there to be alicorn colts?" His thoughts were cut short as he heard muffled voices approaching from outside. Sky decides to quickly hides behind one of the huge support pillars, and the giant doors open.
"Sire, are you sure you want to go right away? I mean, I know that the prophecy is being fulfilled, but from what I've studied of the transcripts-" explains a small white colt with a slightly disheveled light blue mane, only to be cut off by the spreading of wings. Wings similar to those of the portrait near the front belonging to the alicorn king of the past.
"I do not wish to hear about your mess and troubles! Alert all of the country, Messi Nizer! It is time to claim our new home." Says the older pony, turning just enough for Sky to see he was an alicorn. His horn was slightly curved, just like how King Sombra's was.
"Y-y-yes King Shadin!" Messi bows quickly, rushing out of the large hall, the doors shutting behind him. King Shadin walks over to the throne, looking at the damaged portrait.
"I hope you enjoyed your home, dear sister. Because after I conquer this land...I'll be coming for you." He says, dark swirling must flowing from around is crimson eyes.
****
"AAAH!" Sky yells with a start, looking around see it was slightly dark. He was back in the Cave of Harmony?
"What kind of nightmare was that!? I might it be able to..." He soon trails off after seeing the silver light again, shining bright. He reaches down into the dirt, pulling out what appeared to be a a simple rock. Upon further inspection though, it had a unique design embedded in it. Six circles, each one colored differently from the others, connected to what appeared to be a silver and blue diamond in the center of the spheres.

Unity...

"Huh?" Sky looks around, but doesn't see anyone. As he was about to call out, bells start sounding off in the distance.
"Oh dang it! I'm late for the ceremony!" He quickly flies out, carrying the stone with him in his saddle bag. Little did Sky realize, this stone would define his future in many ways.