Cersei and Tyrion agreed to make Gendry king, because Gendry is Cersei’s son
We saved one of the best for last. Many have speculated about what exactly Tyrion and Cersei discussed behind closed doors in the season 7 finale, “The Dragon and the Wolf.” One theory supposes that the Lannister siblings decided that Gendry — the fastest bastard in Westeros — will be the next ruler of the Seven Kingdoms. Because Gendry, if you didn’t know, is actually Cersei’s firstborn child with Robert Baratheon, the black-haired son she told Catelyn Stark died in infancy way back in the second episode of the show.
That escalated quickly.
While Gendry doesn’t recall much about his mother, he remembers she had “yellow hair.” Also, he’s lived in King’s Landing his whole life, a city Cersei claims she knows everything about. Does all that add up to him being Cersei’s secret son? We’re not sure, but it sounds downright plausible compared to the next part.
When Cersei and Tyrion meet in private, the theory goes, she reveals this, and they make a deal to seat Gendry on the Iron Throne when things are all said and done, once Daenerys has presumably perished fighting the Night King, or is deposed. Under this theory, Tyrion has lost faith in Dany and is willing to plot against her.
If we had to choose one part of this theory that’s the most implausible, it’s the idea that Cersei would give up the Iron Throne to ANYONE. Have you met her?