Warning: SPOILERS ahead for Supergirl season 5, episode 15 "Reality Bytes."
Supergirl had its latest episode wrap-up a forgotten arc from season 2 that hit close to home for both Alex (Chyler Leigh) and Kara Danvers (Melissa Benoist). One of the Superman veterans that joined the Arrowverse drama back in season 1 was Lois & Clark: The New Adventures of Superman star Dean Cain, as part of a legacy casting. Having formerly played the Man of Steel, Cain joined the series as Alex's father as well as being a surrogate dad for Kara. While serving as a guest recurring player, Jeremiah had a significant part during the first two seasons. After having been pressured by Hank Henshaw (David Harewood), Jeremiah left his family to join the D.E.O. in order to protect Kara.
But despite being believed to be dead, it turned out that Jeremiah had landed in the hands of Project Cadmus. Led by Lillian Luthor (Brenda Strong), Jeremiah ended up working for the evil organization during the second season. What followed was a complicated arc for the scientist as Jeremiah had been put in an impossible situation. During the two episodes "Homecoming" and "Exodus", Jeremiah had to go against his family and friends. Lillian had blackmailed him into working for her as she'd hurt Alex and Kara if he didn't comply. After trying to infiltrate the D.E.O., a temporary war against Jeremiah began.
Once it was revealed that Jeremiah, despite doing Lillian's bidding, was trying to oppose Cadmus, things took a bad turn. Jeremiah's last on-screen moment happened in the later parts of "Exodus" as he had a brief showdown with Cyborg Superman. Following that episode, Supergirl seemed to have dropped his storyline as the next three seasons excluded that plot. Aside from a few references in season 3, the mystery behind Jeremiah's whereabouts was left unresolved until this season. In the 15the episode "Reality Bytes," the hour came with an unexpected update on Cain's character.
In one of the final scenes, Alex gets a phone call from her mother Eliza (Helen Slater.) While viewers never get to hear the phone call, Alex goes to tell Kara some shocking news. Shaken by what she had just learned, Alex reveals to Kara that they had found Jeremiah's dead body as she begins to tear up. "Reality Bytes" never specifies how he had died or where he had been this entire time since season 2. It's possible more details about his offscreen death will be revealed in next week's episode, titled "Alex in Wonderland." It's unclear why Supergirl decided to bring closure to that unsolved storyline from almost three seasons ago.
Jeremiah's missing whereabouts haven't been touched upon in a while. That's what makes his off-screen passing that much more surprising as it came out of the blue. Given the packed storylines in the last seasons, it may have been difficult to work in a resolution to Jeremiah's disappearance on-screen. Seemingly, it may never have been an issue of actor availability. Cain expressed interest to return to Supergirl and even partake in Crisis on Infinite Earths during an ET Tonight interview in 2019. But despite being open for it, it seems like TPTB of Supergirl has chosen to conclude the character's time in the Arrowverse for good.