Arwen faced a tough decision throughout The Lord of the Rings -- leave Middle-earth with her people or stay and live a shorter life with Aragorn. However, despite Elrond's warnings of a depressing mortal existence, Arwen chooses to remain with the love of her life. And that has left fans to wonder what happened to her after the war.
The Lord of the Rings: The Return of the King sees Arwen reunite with Aragorn at his coronation. And as the Elves sail away into the West, she stays to marry Aragorn and becomes Queen of Gondor. She even gives her place on the boat to Frodo, one of the last people to leave Middle-earth and visit the Undying Lands. That left Arwen as one of the few Elves still on the continent, with the other remaining few mostly being Wood Elves who preferred the forests.
But with the story ending in Return of the King, author J.R.R. Tolkien wrote about many characters' lives after the war. The appendix reveals that because of his heritage, Aragorn also became king of Arnor. However, the area had become ravaged by the war, and as queen, Arwen had to help return the kingdom to what it once was and restore the population it had hundreds of years ago. The books also reveal that for many years after the war, Gondor and Arnor prospered and had help from the Dwarves with rebuilding.
Only a year after Sauron's defeat, Arwen and Aragorn had their first child -- Eldarion. He was the one and only son they had, but the couple did have several unnamed daughters in the years following. But throughout the Fourth Age, physical age began to catch up with Arwen and Aragorn, and their son became next in line for the throne. Aragorn's lineage came from the Dunedain, an old race of Men who differed from the rest. That meant he was stronger, more intelligent and healthier and had a longer lifespan. But still, he could only live for a couple of hundred years, so Arwen had to make another tough decision.
Most Elves had no choice in their lifespan and had to accept their immortality. But because of who Arwen descended from, she was given the rare opportunity of choosing what she wanted. Her great-great-grandmother, Luthien, was an Elf who married a Man by the name of Baren, and because of this, she had a mortal bloodline within her and was somehow able to accept mortality if she so wished.
After being together for 121 years, Aragorn finally passed away at the age of 210. And within a year, Arwen died from a broken heart and was buried next to her husband. But their son Eldarion continued their legacy and served as proof that Arwen got the mortal life with Aragorn she had always wanted.