Based on the alternate dimension of King Sombra within "The Cutie Re-Mark."

In my years of working under her command, Princess Celestia had always been a beacon of strength and hope for Equestria and it's military. However, during the Second Great War, I saw something no other pony got to see. It's a side of her I will never forget.

Based on the song "The Last Stand" and other various references by Sabaton.