Talk:Episodes, films, and shorts/@comment-5288784-20160327161932/@comment-5288784-20160330111230

In recent tweets AK Rogers confirmed Celestia and Luna were intended to be alicorns by birth. There were certain hints in the Journatl, but it's nice to have definitive confirmation.

Regardless, even if they too were awarded alicorn status at some point in their lives, we already knew they were alicorns when asked to be the princesses of Equestria, which means Celestia's statement in season 6 premiere was always in harmony with other official sources.

The only curious statement came from Luna. Somehow they didn't expect that an alicorn can give birth to an alicorn – and that's the real mystery which we can only speculate about. Certainly it didn't happen in the history of Equestria, but why? Perhaps this will be explained another time, but here are some possibilities.
 * A curse or other ailment affected alicorns and their breeding capabilities. (as explained above)
 * Because, simply, it has never happened… by choice. Celestia nor Luna never had any foal. Cadance is the first artificial alicorn to have one (or perhaps even the first artificial alicorn ever) and the princesses weren't sure if the offspring of an artificial alicorn can be an alicorn oneself. This is a similar theory to the one by AK Rogers, although it provides no explanation as to what had happened to the ancient alicorns.

PS: This has become a little lengthy at it will get buried eventually here in the comments, so I'll move it to a blog.