The Cakes reveal that they are Pinkie's real parents.

Decided to do this idea as soon as I thought of it. Pinkie was always very different from the rest of the Pie family, being that one little ray of sunshine in their otherwise boring, gray, and dull lives. And for the longest time, she never questioned it, but what if there was an actual reason for that? One more closer to her than she thought? Chiffon Swirl and Carrot Cake had Pinkie when they were both quite young, and at the time, they didn't have the means to take care of her. With heavy hearts, they put her up for adoption, where she was taken in by the Pies. Igneous and Cloudy were rather lazy with naming her and simply called her "Pinkie" due to how pink she was. The Cakes bid their first little filly farewell and moved on with their lives, though the love they had for her never wavered.

Years later, when Pinkie grew up and left the rock farm for Ponyville, she stepped into Sugarcube Corner, seeking a job and a place to live. The Cakes were shocked that their baby girl had somehow found her way back into their lives, but didn't know how to tell her who they really were. They concealed the secret for a while until one rainy day, when Pinkie happened to discover their photo album.

Another fun "what if" scenario. Pinkie always looked as if she related more to the Cakes than the Pies, and it would have been interesting if this were the precise reason why.