Discord grows up as an honorary sibling of Celestia, Luna and Cadance, they are all very close and do almost everything together. Until the day Celestia (and sort of Luna) calls him a monster. (this also involves a reason why Luna became Nightmare Moon around the same time, but I don't full explain that, you have to figure it out, but it shouldn't be to hard). I do not own the cover art.
*This contains no shipping*
Special thanks to Silver Flash, who doesn't own an account but wrote this with me