WARNING: The following contains spoilers for Rick and Morty Season 5, Episode 8, "Rickternal Friendshine of the Spotless Mort," which aired Sunday on Adult Swim.
It's no secret that Rick is a terrible father, and he even admits to this after learning that he didn't pay attention to which version of Beth was real and which was a clone. On top of that, he abandoned Beth for years, giving her trust issues that are still present to this day. However, as revealed in Rick and Morty Season 5, Episode 8, "Rickternal Friendshine of the Spotless Mort," this history between Rick and Beth is darker than originally expected.
In this Rick and Morty episode, Rick enters Birdperson's subconscious in hopes of bringing him back to life. As he journeys through his best friend's mind, he runs into a younger version of himself. The two team up as they memory hop, and in the midst of this, the main Rick name drops Morty. The younger Rick is surprised they have a grandson, and this isn't just because Rick returned to Beth and developed a relationship with her family.
"You’re one of those creeps who moves in with abandoned adult Beths," the younger Rick asks. "You live with a version of our dead daughter."
According to this younger Rick, their Beth died sometime before Rick met Birdperson. Instead of accepting the death of his daughter, the older Rick appears to have moved in with an alternate version of Beth, one who didn't die and was abandoned by her Rick.
What's even more telling is that Rick does not deny this. He may think this claim is so ridiculous that he doesn't need to respond; however, his silence speaks volumes, especially when looking back at Rick and Morty Season 3, Episode 1, "The Rickshank Redemption." Similar to "Rickternal Friendshine of the Spotless Mort," this episode is about entering one's memories, with an agent of the Galactic Federation entering Rick's mind in hopes of uncovering the secrets of the portal gun.
Rick agrees to show the agent the moment where he discovered interdimensional travel, and this "memory" features a younger Rick witnessing his wife and Beth die brutally. This prompts the scientist to perfect interdimensional travel, presumably to find a new version of his family. However, in "The Rickshank Redemption," Rick exhibits immense control in his mind, as he's able to manipulate what's happening around them.
Until now, it seemed like this was a false memory created to deceive the Galactic Federation, as he even claimed this was a fabricated origin story. However, after the revelation in "Rickternal Friendshine of the Spotless Mort," it seems this trap may have held some truth. After his wife and Beth's death, Rick would perfect his portal gun and travel across dimensions, meeting Birdperson along the way. Theoretically, after years of doing this, he'd eventually decide to reunite with "his" daughter, finding a Beth whose Rick walked out on her, taking his place.
This also wouldn't be out of the ordinary for Rick. In Rick and Morty Season 1, Episode 6, "Rick Potion No. 9," a love potion made for Morty turns nearly everyone into deadly, mutated monsters, and there is no fixing this. Instead of living in this world, Rick decides they should go to a new dimension where alternate versions of themselves are dead. He even has a device that can scout for dimensions where alternate versions of himself and others die, making it easy to slide in and take their places.
While this traumatizes Morty, Rick is unphased. Initially it seems like this is simply because Rick is often someone who doesn't develop attachments to others. However, with what the younger Rick said, the scientist's cool demeanor here could be because he's already done this before, replacing another Rick to finally be reunited with his family.
Rick and Beth's past was already dark, but knowing that Rick's actual daughter died and he took over another Rick's life so he could develop a relationship with an alternate Beth takes things to another level, especially since he's keeping this a secret from the Smiths. It is possible that Rick could own up to this, but with the Rick and Morty Season 5 finale on the horizon, as part one airs September 5 at 11:00 pm on Adult Swim, this would be a huge bomb to drop on the Smiths.