There are many things Twilight learned while reading books, like spells and dark magic. Star Swirls last book was dark magic and she will find out why.

Alone, that was my destiny and it was sealed by the spell that made me an alicorn. "From one to another, another to one. A mark of one's destiny singled out alone, fulfilled." I sealed my fate, with an upside down pentagram, the sign of antichrists. The defiance of god.