Game of Thrones - Jon theories

Some theories about Jon who is now officially no longer a Snow, but a Targaryen.
So, obviously, he is one of the most represented characters in theories, because he will certainly play a major role in the eight and final season and we can assume, he will also be a main protagonist in the show’s finale.

We all know by now what the R+L=J theory states. But where did it come from?
People may think this theory developed during seasons 5 and 6 of the show, but in reality, it is much, much older.

This is a popular theory, claiming that Jon is indeed the Prince that was promised.
It’s an easy-to-support theory, because it is based on relatively solid foundations and this quite plausible. It is not without flaws though, but since it is based on a legend, some flaws are to be expected.