Dear Cup Cake,

You're a cheating, lying slut. So your great aunt's second cousin twice removed was a pegasus? Then how did those genes get passed down to you? And I may not know much about genetics, but I know a lot about not making sense, and while I can see an atavism occurring several generations later, I don't think an entire breed of pony will pop up after five or six generations of earth ponies.

Yours sincerely, Discord