Celestia, tired of Blueblood bringing self-serving acts of Parliament to her to sign, is thoroughly surprised when he brings her a declaration of war on Twilight Sparkle, freshly-coronated Princess of Friendship.

(Can be set about anywhere in S4, though very little is required to place it besides it being relatively shortly after Twilight's crowning. Tirek won't have happened yet, but the consequences are terribly minor.)

[spoiler]There is an equivocation pun in the title.[/spoiler]