Game Of Thrones' episode "Eastwatch" was heavy on reunions and planning, but it also managed to drop a game-changing piece of information. Unfortunately, nobody but the viewers heard it. If Sam learns the truth about Jon Snow's parents from Gilly, then he could end the war between Cersei and Dany and completely change the course of the show. But if Sam is going to get this crucial information, he's going to need to be a better listener.
As the saying goes, "If a marriage is had and nobody hears about it, is Jon Snow still the rightful heir to the Iron Throne?" Gilly's discovery of the secret annulment and remarriage of Rhaegar Targaryen proves that Jon Snow is not a bastard, and is the rightful son of the former heir to the Iron Throne. This would mean that Jon has an even stronger claim to the throne than Daenerys. Unfortunately, none of this can be acted on if nobody knows about it. Jon Snow and those that support him have all the pieces of a puzzle that, once solved, results in him being the rightful king of Westeros. But first, Sam needs to know that the information is right under his nose.
Sam's headstrong nature and willingness to help save the Seven Kingdoms is what brought him to Oldtown, even if his internship wasn't what he expected. Trying to find useful information in his workload is like finding a needle in a Drogon-sized haystack. However, mere moments before Gilly found the needly, Sam decided that enough is enough and that they should head to Eastwatch. If he hadn't decided to leave at that exact time, he would've heard one of the most important lines in the entire series.
If Sam had waited just a few seconds, he would've heard that Prince "Ragger" had an annulment and remarriage ceremony in Dorne (likely to Lyanna Stark). But, Jon isn't the first heir to a throne that has been snuffed out or ignored. Gendry, who recently reappeared hiding in plain sight in King's Landing, is more of a rightful heir to Robert Baratheon's throne than Cersei. However, the truth doesn't matter much when nobody knows what it is. If Sam does find out about Jon's true parentage and the legitimacy of his birth, he's going to have to travel Westeros with a handy flowchart just to explain what really happened to everyone. And, let's remember, nobody but Bran knows that Ned isn't Jon's father — so even if Sam had listened, he wouldn't have put two and two together.
While Sam is almost aware of Jon's true parentage, he's still not the person most likely to reveal that information to him. The person who is currently most likely to inform Jon that he's a Targaryen is none other than his adopted brother Bran. While Bran is deep in the throws of his Three-Eyed Raven phase, having access to all knowledge in Westeros means that he already knows the truth about Jon. Now we just have to hope the Stark brothers meet up again soon.
