This MLP AU centers around the Great Crystal War between King Sombra and Queen Celestia, where it was eventually won by Equestria, but not without great cost and devastation.  
Queen Celestia, Luna, and Cadence were killed in the War when Prince Solar Radiance and Prince Orion were only teens, thrusting them into a kingship that neither was fully ready for.
 
King Solar Radiance (formerly Prince), is the son of Celestia and alternate!Sombra (from the comics), where Celestia discovered she was pregnant after returning from the mirror. Since he would one day be ruler, Celestia gave him a strong and bold name to fit into. He is the ruler of the dawn, and while he was named after the sun, his ironically dark colors symbolize how unfitting he is to actually lead an entire country at such a young and inexperienced age.  
Several years older than Orion, he is the strongest and most capable of the two, much like how Celestia was once regarded as the main ruler, and Luna as co-ruler.  
Personality: Strict and fierce like a grizzly bear when need be, but a gentle giant otherwise. He is also the most mature of the two and often worries for Orion’s future, much as an older brother would. It was he who saved Orion from much of the fighting and from certain death. He is a noble prince, slow to anger, and genuinely wishes the best for his country.  
Special talent: While Orion is fixated on flashy magic and brewing spells, Orion is much more physical and relies on endurance and brute strength. Before ascending to the throne, he was Lieutenant General with Flash Sentry as General, and took over the position after his untimely death.