People simply can't stop talking about the premiere episode of House of the Dragon for many reasons but the most important one is pretty obvious. During the Red Keep scene, Viserys I Targaryen revealed the truth about the Song of Ice and Fire. It was an eye-opening revelation that Ryan Condal has confirmed to have been approved by George R.R. Martin himself!
After deciding to name his daughter as his successor, Viserys took Rhaenyra Targaryen to the Red Keep where he tells the princess about Aegon the Conqueror's reason for conquering then uniting the seven kingdoms. As it turns out, Aegon had a vision of the fall of man and needed to ensure that Westeros was united when the Long Night finally came. Aegon called his dream "The Song of Ice and Fire" and prophesized that a Targaryen should be on the Iron Throne to lead Westoros in the fight against the White Walkers.
As mentioned, it was a huge reference to the future that we saw in Game of Thrones and the idea of incorporating Aegon's dream in House of the Dragon came from George R.R. Martin.
“That actually came from [Martin], at least the origin of that point,” co-showrunner Ryan Condal told Polygon. “He told us very early on in the room — just as he does, just casually mentioned the fact that Aegon the Conqueror was a dreamer who saw a vision of the White Walkers coming across the wall and sweeping over the land with cold and darkness. [...] So with his permission, of course, we infused that into the story because it was such a great way to create resonance with the original show.”
It's awesome to know that George R.R. Martin wanted Aegon's dream to be a huge part of House of the Dragon. With that in mind, we are looking forward to learning more about the vision in the upcoming episodes.