Had this idea

Before friendship is magic chrysalis leaves a baby changling on twilights parents doorstep
It’s twilight unaware she is a changling

Chrysalis did it not wanting her to starve

Canterlot wedding the spell reveals her as a changling princess (young Queen who looks like a changling nymph mixed with chrysalis)

Another idea
Chrysalis is also secretly twilight velvet 🤣

(Though this would be notice able and weird
Since at the canterlot wedding she cannot be candance and twilight velvet at the same time 🤦🏻‍♂️🤣 unless another changling took her place )

7862945
That has actually been done I think, the first one at least. Give me a minute I'm going to find it.
Edit: found it! The reason is slightly different, but essentially the same premise https://www.fimfiction.net/story/284555/change

there's a couple of stories with the first premise, some good, some less good, but still interesting

Mirrors Image
Not the doorstep. Twilight was a stillborn who 'miraculously' came back to life.
We never did get the sequel that was supposed to actually finish the story.

Good premise, but has been done at least twice to my knowledge in two good stories “Change” and I believe “ Mirrors Image”.