This story is told in the words of Pinkie Pie's father detailing the back story of when she got her cutie mark.

"You know of my daughter, yes? I'm sure you do. She makes herself known to everypony. My little daughter - I love her very much in the same way she loves everyone else. She knows more about others than they do about her. Perhaps her story should be expanded upon in her father's words."

To a father growing old nothing is dearer than a daughter - Euripides