Check out my latest Game of Thrones Season 7 Theory, Has Rhaegar Targaryen Already Saved Westeros!?
The Theory starts of by going back to the Doom of Valyria and covers the Three Heads of the Dragon Prophecy, The Prince That Was Promised Theory, and digs deep in to the realm of A Song of Ice and Fire.
This is definitely one of my favourite Rhaegar theories but I would say it was more based on ASOIAF rather than the TV Show.
Video credits to Game of Theories YouTube channel