Celestia and Luna married the mane six, now they have a harem and a honeymoon to deal with. In all honesty, happily ever after isn't all it's cracked up to be. At least there'll be room for orgies.
Have you ever gotten so drunk you forgot you offered the princesses' hoof in marriage to whoever brought your sister back? And how many 'es' there are in 'Princess'?
Pinkie Pie is sorely missing Braeburn, so Rainbow Dash offers to take her out to Appleloosa to pay him a visit. Unknown to both of them, Braeburn has other ideas...