Well, it's more of a spin off of a small part of it. Bet you can't guess.
During Discords last reign he accidentally tripped a magic tripwire of sorts that was supposed to go off when he was stopped the first time however that didn't happen. Now the ancient and forgotten race of ponies known as the Hippocampus (Sea Ponies) are awake from over a thousand years of sleep. The new King Saris needs to rebuild his family's former empire and try really hard not to use his newfound powers to kill Discord.
Bit of warning: ancient race means Equestria's history, means a bit of head cannon.