Warning: The following contains major spoilers for the Game of Thrones Season 7 finale.
While the latter didn't exactly feel like breaking news (Gilly had practically spelled it out earlier this season), the knowledge that Jon, and likely Daenerys (Emilia Clarke), will learn of his true heritage as soon as they make it to Winterfell is incredibly exciting. That's because these reveals have far more ramifications than simply giving Jon the sense of identity and belonging he craved growing up.
Let's break down exactly why this twist matters -- and what that means for the show moving forward.
The historical significance of the name Aegon: As anyone with a knack for Westerosi history knows, Aegon is an incredibly important name in the Targaryen family. It was Dany and Jon's ancestor Aegon the Conqueror who journeyed from Essos to Westeros and, in case you couldn't tell by his name, conquered it and united its people into one kingdom. Since then, Aegon has become a common family name within the Targaryen clan, but revealing that Jon was named after the famed conqueror could hint that he's the one who is truly destined to unite humanity against the Night King and save Westeros -- not Daenerys.
The mystical significance of the name Aegon: If you, too, were confused by the reveal that Rhaegar apparently had two sons named Aegon, you are not alone. If you remember, Rhaegar had two children with his first wife, Elia Martell, named Rhaenys and Aegon. After Rhaegar was struck down by Robert Baratheon, The Mountain killed Rhaegar's children as well as Elia during the Sack of King's Landing. (These were the children Oberyn Martell was out to avenge in Season 4.)
All of this makes Lyanna's decision to name her own son with Rhaegar after his recently deceased son Aegon a bit odd, to say the least. However, she actually may have had very good reason to do so.
In the books, during Daenerys' sojourn to the House of the Undying she has a series of visions, including one of Rhaegar naming his son Aegon, explaining that he is "the prince that was promised" and "the song of ice and fire." If Lyanna were aware of Rhaegar's belief that his son Aegon would be destined to save humanity, then she might have chosen to name their son Aegon in the wake of the first Aegon's death, thus doing her part to ensure that the prophecy comes true.
If this prophecy is to be believed, then this would seemingly all but confirm that it's Jon, not Daenerys, who is Azor Ahai, which would mean Daenerys will now find herself without a grand, fated destiny and without a rightful claim to the throne, which brings us to...
The political ramifications of the reveal: Daenerys wants to use her power to achieve a lot of noble things like "breaking the wheel" and freeing the oppressed, but her entire justification for her invasion is that she is simply reclaiming what is rightfully hers: the Iron Throne. The reveal that it's actually Jon who is the true heir puts a major wrench in her plan -- something which is sure to ruffle her feathers, despite her growing feelings for her nephew.
There is absolutely no way Dany will be fine abdicating her claim to Jon, nor will she be fine sharing the Iron Throne (as pointed out by Clarke herself). She wants to be queen of the Seven Kingdoms, not co-queen. The realization that Jon is technically not just an ally, but a potential threat to her rule could potentially sow dissent between the pair, but we wouldn't count on it.
Jon has never wanted to rule anything. He never asked to be Lord Commander of the Night's Watch. Sam (John Bradley) championed him. He never asked to be King in the North. Lyanna Mormont (Bella Ramsey) made that happen. Jon is a simple man with a strong moral code. All he wants is to defeat the Night King and live an honest life. Lest we forget, the finale made it abundantly clear how much Jon's willing to sacrifice in the name of sticking to his word, and so we doubt he'll decide to break his oath to Dany simply because he discovers he has a claim to power -- something he has never shown the slightest inkling in.
In fact, if Jon's true heritage becomes public knowledge and he throws his full weight behind Dany it might actually help strengthen Daenerys' claim because two Targaryens are definitely better than one. What Jon might lose in the process, however, is his claim to the North. He already wasn't a legitimate heir to Winterfell when he was elected King in the North, so it's unclear how much the northern lords would care if he is revealed to be Lyanna's son instead of Ned's. But let's be real, if Jon winds up wanting to marry Dany, he'd have to give up that title and go to King's Landing to be her king anyways. That's why we have a feeling that, for one reason or another, Sansa (Sophie Turner) will be getting her wish and officially taking charge of the North next season.
The personal ramifications of the reveal: It's no coincidence that Game of Thrones spelled out Jon and Daenerys' familial relationship just as they were taking a trip to bone town. They were taking no chances when it comes to making sure every single viewer knew this relationship is incest (although it remains unclear whether or not we're supposed to be OK with that). Targaryens have a long history of incest in the name of keeping their bloodline "pure," and it seems this family tradition isn't going anywhere since we're about 99.9 percent sure that boat sex is going to result in Dany getting pregnant with her nephew's son.
That means even if Jon and Dany decide to squash their burgeoning relationship after realizing they're related, they'll still have ensured the continuation of the Targaryen line through their child together. This would be horrible news for Tyrion (Peter Dinklage), who has been pushing for Dany to turn Westeros into a democracy, and a baby -- a (nearly) pureblood Targaryen baby to boot -- could change her mind and inspire her to want to keep the crown in the family.
As for how Jon will feel about learning of his true parentage, he'll likely be fairly shocked, but his world won't be completely turned upside down. Even more than inspiring Theon (Alfie Allen) to go rescue Yara (Gemma Whelan), Jon's discussion with the former Stark ward in the finale was clearly setting the stage for Jon to accept both sides of his lineage, Stark and Targaryen. As Jon stated himself, "you don't have to choose" between the two sides of your identity. And to be honest, the disparity between Stark and Greyjoy is far greater than between Stark and Targaryen, and so if Theon can reconcile the two, it should be fairly easy for Jon.