Season six of Game of Thrones ends with the coronation of a new ruler of the Seven Kingdoms: HBIC herself, Cersei Lannister. And while her power grab is borne from the literal ashes of tragedy (that she causes), it turns out that according to the Lannister family tree, Cersei sitting on the Iron Throne might not be such a coup after all, as expertly pointed out by Mashable.
After seeing poor baby Tommen go out the window after his wife and a significant portion of the population of King's Landing get burned up by wildfire, you were probably wondering who the throne would go to anyway. After all, Tommen had been the last of Cersei's surviving children. And while sure, Cersei has technically been queen before as the wife of Robert Baratheon, you probably called foul on her just claiming the throne that only belonged to her son because he was a "Baratheon." Technically, by order of succession, the Iron Throne should go to a surviving Baratheon . . . only problem is, there aren't any left. (And yes, we haven't forgotten about Gendry. We're talking legitimate Baratheons here, not bastards. No matter how pretty they are.)
To understand how this all leads to Cersei, we have to go pretty far back into Lannister and Baratheon history, way back to Robert Baratheon's great-great-great-grandfather Arion Baratheon, almost a century and a half before Robert was even born. One of his descendants, Elyanna Baratheon, married a man called Mathis Lannister, binding the Lannister and Baratheon family lines together. Skip several generations down the line, and we get to Tytos Lannister, the father of Tywin Lannister. Bingo.
So if we're sticking with the idea that the Baratheons still have the rightful claim to the throne, then the rightful ruler would be one of Tywin's children: Jaime, Cersei, or Tyrion, who all come from a line that technically goes back to a Baratheon. Jaime Lannister, by virtue of being a member of the Kingsguard, is never allowed to inherit anything or marry and have children. Now, Tommen technically fired Jaime from the Kingsguard in season six and also immediately sent Jaime away to the Twins, allowing Cersei time to claim the throne instead. But even if Jaime had brought up the convoluted reasoning behind his claim to the throne, would he even want to be king? He had his chance after killing the Mad King, and he didn't take it.
So, if we count out Jaime, the Baratheon claim to the throne would then pass to Tywin's next son, Tyrion Lannister. However, Tyrion is not only far from King's Landing (although it looks like he'll be back soon . . . ish), he's also been convicted of regicide. Remember, he chose a trial by combat in season four, and we all remember the Mountain vs. the Viper. Sob.
So if Tyrion is also out by default, then the only one left over from that ancient Baratheon/Lannister line after Tommen's death is Cersei. The Baratheon genes from ancient ancestors combined with the Lannister balls that her dad would probably have been grudgingly proud of. Now, who's to say whether she's even aware of her true lineage? She's likely purely basing her claim to the throne on being the only relative to Tommen left. It sure would be interesting if she tried to use her lineage as proof, though.
However, regardless of her reasoning, Cersei's still in a position to do some real damage in season seven of Game of Thrones, especially if the whole Mad Queen theory plays out. And if that all happens, it might lead to some serious sibling arguments, which as anyone who knows Cersei's prophecy knows, won't turn out well for her at all. Only time will tell.