While Celestia was defending Canterlot from Chrysalis, one of her spells hits a mirror and splits into four, hitting her, Luna, Discord, and Queen Chrysalis. Cadence arrived on the scene, and now is the mother of four, very powerful foals.

Having no idea how to handle babysitting Changelings, or Draconequus, she leaves Shining Armor to watch over the Crystal Empire and heads to Ponyville to ask six very important ponies what to do.

I mean, a spell that got divided between four can't be permanent, can it?