On the day of the Summer Sun Celebration, Nightmare Moon returned from her banishment. The power she had accumulated during her stay on the moon proved to be too great for Princess Celestia, and Equestria's ruler was defeated.
Weeks later, Anon arrived in Equestria via unknown means. Although lost and confused, his natural resistance to magic made him quite useful to Nightmare Moon. To his surprise, he quickly became one of her most trusted servants and found himself falling in love with her. Even more surprisingly, it seemed like she was doing the same.
Eventually, despite Anon's best efforts, Nightmare Moon was defeated and Princess Luna returned. Everyone was rejoicing. Everyone... except him. Because Anon did not fall in love with Princess Luna.
Anon fell in love with Nightmare Moon.