How and when did Lionel (John Glover) discover that Clark (Tom Welling) was the Last Son of Krypton in Smallville? The Kents tried for a long time to keep both of the Luthors from finding out the truth about Clark’s powers, but it was confirmed in a season 5 episode of the Superman prequel series that Lionel already knew.
The devious billionaire and father of Michael Rosenbaum’s Lex Luthor was regarded as a great threat to Clark’s secret, especially by Jonathan Kent (John Schneider). Beginning in season 2, the villain began taking steps to learn more about him, but the main characters, fortunately, managed to avoid him finding out too much. Beginning in season 4, Lionel’s behavior started to change, and his motivations for everything that he did became less clear. Then, everything changed in the show’s fifth season when it was confirmed Lionel was aware of Clark’s secret. When revealing this information to Jonathan, accidentally triggering Jonathan’s fatal heart attack. Several episodes later, Lionel admitted to knowing everything and slowly evolved into a highly capable and resourceful ally.
There’s some confusion from fans over exactly when and how Lionel learned about Clark’s Kryptonian heritage. Lionel told Clark that him finding out everything was a result of him becoming possessed by Jor-El via the Water stone in the Smallville season 4 finale. However, this conflicts with what Tess (Cassidy Freeman) said in season 8, which is that Lionel figured it out shortly after the meteor shower that brought Clark to Smallville. She thinks that because of his involvement with Veritas, he already knew about the coming of a “Traveler,” and that Jonathan asking him to arrange an illegal adoption for Clark tipped him off to the truth.
There are holes in her theory that indicate that Lionel did not know all along. Lionel’s curiosity, frustration, and uncertainty when it came to Clark made it apparent that he didn’t have all the pieces of the puzzle in the early seasons. His perceptiveness made him realize Clark was an extraordinary individual, but that was all he could be sure of. The fact that he ordered Chloe to use her truth-inducing powers to ask the Kents about his origins in season 3 suggests he may have suspected, but still didn’t know everything at this point. The lengths Lionel went to unravel the mystery of Clark Kent wouldn’t make sense if he had all the answers.
All things considered, it’s most likely that Lionel was telling the truth about when he uncovered Clark’s secret. Having Jor-El’s conscience within his mind left him with an untold amount of knowledge about Krypton and its history, including the details about Clark’s real identity. When Jor-El left his body, Lionel returned as a changed man with a new understanding about his purpose in the world. Only when he came out of his trance-like state at the end of Smallville season 5’s third episode did he really know the whole truth. Thanks to having this knowledge as well as the belief that he was an important part of Clark’s destiny, Lionel developed a new role in his life and became devoted to helping him succeed.
