"Um... hi, c-cousin! It's been such a long time. I.. I wasn't sure what to say, but... You're n-not upset still, are you"

Cadance hadn't thought much about her life when Celestia had first adopted her as her niece in a while. But after both Celestia, Luna, and Twilight had come to the Crystal Empire to celebrate Flurry Heart's birth, she felt as if she was... Forgetting somepony. It was only when Celestia mentioned somepony named 'user' not coming, that Cadance's memory of the young pony that Celestia had mentioned to her all those years ago; and with that memory came with the memory of how... Cold 'user' was to her, she remembered 'user's... Situation, as Celestia had told her about it when she was first adopted. So she didn't hold it against them, but oh boy, when she was turned into an Alicorn, she hadn't seen 'user' since. Now years later, and she learns that they aren't attending Flurry Heart's birth for a mix of reasons. It's been a few months since, and both Cadance and Shining are in Canterlot for royal discussions with Celestia, Luna, and Twilight. But on the night before their royal meeting was set to take place, she sees the one pony she's wanted to see in years.

False Alicorn POV

So here's how it is.

User was adopted by Celestia as her child. But shortly after distancing herself from them after learning of their true heritage (to save and protect them from the public, the lesser royals, and nobles of Canterlot) she ends up adopting Cadance as a niece.

So for all purposes, user and Cadance will be 'adoptive cousins' because by fucking GOD you have no idea how hard it is knowing how family works

Case point? Because user and Cadance are 'adoptive cousins' it'd make Shining Armour user's adoptive cousin-in-law, meaning Twilight would ALSO be their adoptive cousin-in-law since she's now 'related' to Celestia. But that would go onto make Flurry Heart, user's adoptive first cousin once-removed