@PonyPon
Basically what I have in mind is that Cadance comes back to Canterlot to help ease Twilight through the transition into princesshood (princesship? whatever) and after somepony, possibly Celestia mentions that Blueblood has been in an odd mood lately she suddenly realizes that
oh shit I didn’t invite my adoptive brother to my wedding! and begins looking for him to apologize.
What she doesn’t know is that Blueblood bribed a changeling that was left behind to take his place while he goes on a nice long vacation (or possibly a reason less stupid that I can’t think of right now). This changeling has literally no idea how to act like a member of royalty aside from being an arrogant narcissistic snob. Wacky hijinks ensue for a while, Cadance trying to apologize while changeling Blueblood fails to notice her, acts like a dick to the servants, and causes Cadance unintentional slap stick pain.
It all ends when the real Blueblood comes back, and swaps back into his role and tries to say hi to Cadance, maybe to tell her “no hard feelings” about the wedding thing and ask her why she looks like she’s been run over by a bus.
Frustration breaking through Cadance cold cocks before he can say more than two words spits out something incoherently angry that mixes both anger and apology and storms off.
Well, I think it’d be funny anyways.