Game of Thrones has no shortage of theories. The series has remained unpredictable from the very beginning but the show does frequently use foreshadowing of some sort. As per the latest theory, not Jon Snow, or Daenerys Targaryen or Cersei Lannister but it would be Euron Grayjoy will be the one to sit at the Iron Throne in Game of Thrones season 8.
As per an interesting theory on Reddit, George RR Martin has previously revealed that the ending of Game of Thrones is going to be a "bittersweet." As per the fan, Jon and Daenerys can defeat the Night King but could later get defeated by Euron and his army, this would make the ending, bittersweet.
Furthermore, the Maesters has already discussed a prophecy that stated that the Drowned God would rise up and defeat Aegon Targaryen. It was revealed in Game of Thrones season 7 that Jon Snow's real name is Aegon, so it looks like this prophecy also holds some truth.
In Game of Thrones world, Euron Grayjoy (Pilou Asbæk) is the uncle of Yara and Theon Greyjoy. After murdering his own brother, Balon, Euron takes control of the Salt Throne and with the support of several Ironborn, he seeks to hunt down his nephew and niece.
Check out the fan theory:
In Game of Thrones season 7, after failing to meet Daenerys Targaryen, Euron sails the Iron Fleet to King's Landing, answering the kind invitation of Cersei Lannister. Cersei proposes an allegiance between the crown and the Ironborn which Euron counters with an offer of marriage. Jaime Lannister's sister declines Euron's attempt at the courtship but when he departs, he promises to return with a gift that will eventually win her heart.
In the later episodes of Game of Thrones season 7, Euron returns to King's Landing where he delivers Ellaria and Tyene to Cersei. Ellaria and Tyene were responsible for Cersei's daughter, Myrcella's death. Cersei accepts his proposal of marriage but on one condition — the two can only get married when the war is finally over.
In Game of Thrones, Euron Greyjoy is shown as a powerful character who has his own army. At the same time, now that Jaime Lannister has abandoned Cersei, Euron can actually play his cards and marry Cersei. If these two get married, then he will become the King who will rule not only the Salt Throne but all the Seven Kingdoms.
Game of Thrones season 8 episode 1 will air on HBO and other streaming services like HotStar on April 14, 2019.