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For a while there it looked like Daenerys Targaryen was the last of her bloodline. Her parents were dead, her brother was gold-melted to death, and her son Rhaego was stillborn. Being the Last Targaryen is a fate she seemed to resign herself to, and there's a world of surprise waiting for her when she finds out that her new boyfriend Jon Snow is a member of the family. Season eight will surely deal with the repercussions of there being two Targaryens and only one throne, but a quick history lesson reveals that all along there's been a third option hiding in plain sight.
Since season two there has actually been another Targaryen relative hanging out in Westeros, and while he isn't as closely related to the former royal family as Dany and Jon are, he's super related to the other, more recent regnal line of House Baratheon. As in he's the last Baratheon. A bastard Baratheon. All right, it's Gendry!
Through his father Robert Baratheon, Gendry is a blood cousin to the current Targaryens. More specifically he is Daenerys's second cousin once removed and Jon Snow's third cousin — but those relationships might be complicated by a slight difference in the Targaryen family tree from the books vs. the show.
To accurately trace where Gendry's Targaryen blood comes from, we have to go back to Robert Baratheon's grandmother, who was a full-blooded Targaryen princess named Rhaelle. Rhaelle married Ormund Baratheon and had a son Steffon Barathon, who was father to Renly, Stannis, and Robert. In the books it's more clear that the reason Robert became king after the rebellion was because of this Targaryen connection, which gave him a legal right to take the throne; Rhaelle was the Mad King's aunt and the Targaryen line only continued through her descendants.
However, there's an even deeper connection between the Baratheons and Targaryens that goes waaaay back to the founding of both their houses, and it's kind of a doozy: the founder of House Baratheon was Aegon the Conquerer's brother.
Aegon's father Aerion had a bastard named Orys Baratheon, who by all reports was Aegon's best friend and number one general. During Aegon's conquest, Orys Baratheon killed the Storm King and married his daughter, which is what established House Baratheon as the premier noble house of the Stormlands. This means that all Baratheons are literally from a cadet branch of House Targaryen through Orys, though his extra strong black hair genes made sure that only Targaryens would have those cool silver tresses.
There's room for comparison between Jon Snow/Aegon Targaryen and Aegon the Conqueror, but making friends with a Baratheon bastard who already has Targaryen blood is a close and interesting historical callback for to subtly include. It's probably too late in the show for detailed examination of everyone's family tree, but keep an eye out next season for Gendry to become more important as he joins his cousins Daenerys and Aegon in their war for Westeros.
