There is a lot of speculation going on about Kylo Ren’s history, and some pretty impressive theories are being thrown about. Some people are convinced we’ll see it expanded upon via flashbacks in Episode VIII, but it’s very likely we’ll learn at least some big clues to his past before then.
We’ve heard a rumor about how Kylo learned that Darth Vader was his grandfather, and it seems to have happened much closer to the events of The Force Awakens than many think.
Luke and Ben were still together six years before the events of The Force Awakens.
This brings up some very interesting possibilities about what the “Force Back” scene in TFA means in regards to Rey’s vision. Instead of Rey being there where Kylo and the Knights wiped out the Jedi, it could mean that’s another part of Luke’s saber’s history.
Ben doesn’t know Vader was his grandfather until this time.
He learns about his lineage when he sees a video with Bail Organa talking about it. A rival senator of Leia reveals the news to the entire galaxy in the form of a holo-recording where Leia’s adoptive father is talking about her real parents: Padme and Anakin/Vader. What this kind of news would do to Kylo isn’t known yet, but you can see how he reveres his grandfather in The Force Awakens.
This also brings up some interesting questions of how Kylo got Vader’s helmet. If he didn’t learn that Vader was his grandfather until twenty-eight years after the events of Endor, it’s not likely he and the Knights of Ren were the ones to retrieve it. Either it’s been sitting in the forest for nearly thirty years, or those Acolytes of the Beyond from Aftermath got their hands on it and Kylo gets it from them.
Again, this is just a rumor right now but it sounds like a much more interesting back story for Kylo than some of the theories out there. If he had just recently turned evil in the short years before TFA, then that could open up some very cool expanded universe possibilities about Young Ben.