At this point in Appendix A there’s this whole little story about Aragorn and Arwen, basically a biography of Aragorn. And it’s extremely longwinded, so I’m going to go fast but it’s still going to be long.
We start with Aragorn’s parents, because that’s relevant. Aragorn’s dad grew up in Rivendell and was one of those rangers of the North, sleeping under bushes and stealing pies off of windowsills. He wanted to marry Aragorn’s mom, and Aragorn’s mom’s father (another ranger) was opposed on the grounds that Aragorn’s dad was too old, plus Aragorn’s mom’s dad had a psychic flash that Aragorn’s dad was going to die soon. But it’s all good, because Aragorn’s mom’s mom talked him into letting them marry, because she had a psychic flash that if Aragorn’s dad didn’t marry Aragorn’s mom, then Sauron would win.
So Aragorn’s dad marries Aragorn’s mom, and eighteen moths later there’s a little baby Aragorn, but by then Aragorn’s dad has already been killed by orcs, his work done. Little Aragorn grows up in Rivendell, with the nickname Estel, which isn’t Estelle, it’s totally different. He doesn’t find out about being the Heir of Isildur da da daaah until he’s full-grown because there’s too many orcs out there looking to kill him and better safe than sorry.
Then he turns twenty and Elrond takes him aside and explains how his dead dad’s dead dad’s dead dad blah blah blah was Isildur, and gave him two of the three royal relics of Arnor, the Ring of Barahir, which is a hella old thing from before Numenorian times, and also the shards of Narsil, the broken sword from the Last Alliance. The third royal relic is the ancient Scepter of Annuminas, the holder of which is the king of Arnor, which is a thing Elrond tells Young Aragorn about but doesn’t give him on the grounds that he’s not awesome enough yet.
Still, all this is a lot for Young Aragorn to take in, and after the talk he’s outside, walking around, singing to himself and processing everything, and while he’s singing the song of Beren and Luthien, which is how he calms himself down, whoa, Luthien appears!
Except that it’s not actually Luthien, it’s some other Elf maiden, and they meet cute because he’s all, wow, Luthien, I was just singing about you, and she’s all, I’m not Luthien, Luthien died many thousands of years ago, and he’s like, oh.
And then — I am not making this up — Arwen says that it’s okay, she gets mistaken for Luthien all the time. And she’s actually Arwen, Elrond’s daughter.
Aragorn is like, no way, Elrond doesn’t have a pretty girl daughter, I’ve been in Rivendell most of my life and I’ve never heard of you, does he keep you locked up in a tower? Arwen is like, no, no, I’ve just been visiting my mother’s family in Lorien for the last several decades, and then Aragorn finds out that Arwen isn’t, I dunno, 17, which takes a little getting used to on is part because he’s totes smitten.
Afterwards Aragorn goes to his mother, and she’s like, boy, Arwen? Really? An Elf girl, not a nice Dunedain lady? And he’s all, but she’s so pretty, and besides, aren’t I descended from Isildur, who was descended from Elros the first king of Numenor, whose brother Elrond is Arwen’s dad? So, we’re like, cousins, and she’s not out of my league.
Aragorn’s mom is like, that’s not how that works, but secretly she has a psychic flash of how the two of them eventually get together.
Elrond calls Aragorn in when he hears about this, and by hears about it I mean that Elrond notices Aragorn staring all moon-eyed at Arwen all the time. “Knock it off,” says Elrond.
“Why?” says Aragorn.
“I’ll tell you why,” says Elrond, “we’re under an unexplained mystic fate such that when I go westward to Valinor, Arwen can either come with me and leave you and all of Middle-Earth behind, or she can stay and learn about age. And I do not want her to know about mortality!”
Aragorn kicks the ground and shuffles off, and then he leaves Rivendell and goes off to have adventures out in the world and prove himself. He takes the pseudonym Thorongil, and hangs out with the Rohirrim for a while and then joins the Gondorian army and completely fails to befriend Young Denethor.
Twenty years or so later, Aragorn decides to wrap up his adventuring, and heads back home to Rivendell, by way of Lorien, which he’s never been to before. He meets Galadriel and chills for a while and bumps into Arwen, who happens to be visiting again. She announces a plan to marry him and live with him and then die of grief with him once he dies of old age, which Aragorn thinks is great.
Elrond, though, thinks that’s less great. He comes up with a plan to stymie Aragorn & Arwen’s wedding: he shall only give their union his blessing if Aragorn becomes King of Gondor and also Arnor first, and defeats Sauron once and for all.
So then there’s the War of the Ring, we’re all familiar with that, and afterwards they’re the King and Queen of the Reunited Kingdoms o Arnor and Gondor, and finally like centuries later Aragorn grows old and dies after a heartfelt talk with Arwen about how much they love each other. Then Arwen leaves Gondor and returns to Lorien, which is otherwise empty of elves by this point (Galadriel and Celeborn and so on have already left) and there she lays down and dies. The end!