King Sombra and Queen Crysalis invaded Canterlot, when all hope was nearly lost the bearers of the elements fought desperately but one by one they were entrapped in a crystal resin, Twilight was about to have the same fate but Princess Celestia threw herself in front of her student becoming entrapped herself, with no one left to help her she was overpowered by the evil duo.
She was dragged down to the crystal caverns beneath the castle, Tied to a crystal pillar and left to die a slow death, will insanity seep in before her death and take her or will something else arise from the darkness within, only time will tell.
Is not canon plus there will be gore.
Picture: Just a quick knock up design, if anyone thinks they can design an even better Astral by all means go for it, if you want to copy the looks for your own storys I also don't mind