My Little Pony: Friendship is Magic - Alicornication by ZSparkonequus

Actually, this is the very first time it’s been suggested that a pony can be an alicorn from birth. Both Twilight and Cadance evolved into alicorns, having been born as a unicorn and pegasus, respectively. And as for Celestia and Luna, the show has never given a canonical origin story for either of them, a billion fanfics and fanarts notwithstanding.