Princess Celestia's life has been changed many times by Twilight Sparkle, and always for the better. From being Celestia's most successful protege, to returning her sister Luna to her, to saving Equestria from foes even Celestia could not face, Twilight has been a constant source of joy in her life.

So what happens when Twilight tells the very symbol of Equestrian beauty that she's fat?

Celestia panics, of course!