Admittedly, Luna should have told somepony, but it was such a unique opportunity.

Author's Note:
Feel free to leave constructive criticism in the comments. I literally live for it. Even if it's a bit harsh, after reading it I might get a little upset, but I will just simmer silently about it for a few days before ultimately deciding that you probably have a point.

The source of the cover art can be found here:

http://mlp-headcanons.tumblr.com