this is a drawing for the derpibooru contest
I'm not sure if it qualifies to be honest, because it's filly derpy, but it's one of the first ideas that came to mind
my original premise was that Derpy got lost and Celestia finds and comforts her;
or a bit more heart wrenching, she's an orphan and Celestia is on an annual visit
always open to interpretations of course!