TL;DR version: Tyrion is Dany’s child (Rhaego).
“To go north, you must journey south. To reach the west, you must go east. To go forward you must go back, and to touch the light you must pass beneath the shadow.”
-ACOK, Daenerys III. Spoken by Quaithe.
D+D=T is irrefutably one of the most insane fan theories presented. Created by xyseth on reddit, D+D=T proposes that Tyrion Lannister is in fact Rhaego Targaryen, the supposedly stillborn baby of Dany and Khal Drogo.
What the heck, right? It’s quite the stretch, but xyseth is able to stitch the theory together (with some A+ formatting skills to go with it). You can read the full theory on reddit, but I’ll give you the quick hits here, along with some commentary.
How Tyrion Traveled Through Time
After xyseth posed the theory, it was humorously referred to as the time-traveling fetus theory as well as D+D=T. That’s because the theory rests on the assumption that Tyrion/Rhaego literally traveled through time while still in the womb of Dany Targaryen.
So who opened up a spacetime wormhole and transferred Tyrion from Time A to Time B? Mirri Maz Duur.
The theory posits that Mirri Maz Duur uses Khal Drogo’s soul to transfer Rhaego back in time. Since “only death can pay for life,” as we are reminded numerous times throughout the series, when Rhaego is transported back in time (alive, and containing Drogo’s soul), something must be transported to present day (dead).
The theory says that Rhaego was transported back in time to Joanna Lannister’s womb, as she was already pregnant, and her true child was transported into Dany’s womb. When Dany gave birth, her child “had been dead for years,” we are told by Mirri Maz Duur. Could it be because it had to travel though time?
Thus, when Tyrion Lannister makes his way to Mereen and sees Dany, Drogo (by virtue of his soul being in Tyrion/Rhaego) will have returned to Dany, just as Mirri Maz Duur said (“When the sun rises in the west and sets in the east… Then he will return and not before.”)
“In other words, before Dany’s husband returns, a reversal in time - symbolized by the sun moving in its opposite direction - has to complete. Quaithe, too, has more to say about time travel,” writes xyseth. Quaithe’s quote related to time travel is what began this article.
Therefore, Tyrion is Rhaego, and is the “stallion who will mount the world.” In other words, the theory concludes that Tyrion will become one of the three heads of the dragon and will ultimately ride one of the dragons, thus “mounting the world.”
So, what do you think? This theory is definitely a stretch, but we’ve got to give xyseth credit for actually going to the book to give it some textual support.