The second episode of House of the Dragon makes no mention of Aegon Targaryen's dream of the Long Night and the appearance of the White Walkers in Game of Thrones, despite the series premiere dropping a major bombshell regarding him.

The first episode of House of the Dragon concluded with King Viserys (Paddy Considine) designating Princess Rhaenyra Targaryen (Milly Alcock), his teenage daughter, as the rightful heir to the Iron Throne. The knowledge that Aegon the Conqueror anticipated the Night King's plot to wipe out the male realm in Game of Thrones was made public as a result.

There is a significant retcon in Aegon's dream that affects everything that happens in House of the Dragon and Game of Thrones after it. Viserys asserts that the real reason Aegon and his sister-wives took control of the Seven Kingdoms more than a century before House of the Dragon premiered was not merely for House Targaryen's grandeur, but rather because Aegon had dreams of the arrival of the Night King and the White Walkers.

As a result, Aegon reasoned that House Targaryen needed to rule and unify Westeros since only the Targaryens and their dragons could put an end to the Long Night. However, Aegon the Conqueror was unaware of the precise date of the Long Night.

Therefore, the truth of Aegon's dream was kept a secret that was only passed down from Targaryen King to Targaryen King. Viserys telling Rhaenyra of this great burden was his way of proving that she was his true and sole heir who would succeed him as the first Queen of the Seven Kingdoms. 

Rhaenyra will cling to the facts that Viserys refused to identify anyone else as his legitimate heir and that the lords of Westeros swore their allegiance to her in 112 AC as House of the Dragon progresses and her claim to the Iron Throne is undermined.

The battle between the adult Rhaenyra (Emma D'Arcy) and Alicent (Olivia Cooke), which will still take place in House of the Dragon, is given further depth by Aegon the Conqueror's dream. As per Westeros' patriarchal traditions, once Alicent becomes queen, her children, particularly her firstborn son Prince Aegon (Tom Glynn-Carney), officially replace Rhaenyra as Viserys' heirs.

Because only she is aware that the White Walkers would one day invade the Seven Kingdoms, Rhaenyra's knowledge of Aegon's dream, which intensifies her conviction that she must succeed Viserys and take the Iron Throne after his death.

Whether Rhaenyra will share Aegon's dream with anyone else and how it will be passed down to the Targaryen Kings until the dragon dynasty is overthrown in Game of Thrones are yet unknown.