It took seven seasons, but Lex finally deduced Clark's biggest secret in Smallville. For years, Lex sensed that there was more to Clark than what meets the eye, but couldn't be sure exactly what his friend was keeping from him. But in the season 7 finale, all became clear to him at last when he figured out that Tom Welling's character was the Last Son of Krypton.
Lex had long suspected that Clark had powers of some kind, but one thing that didn't occur to him during their four years of friendship was that Clark might be an alien from another planet. However, this knowledge didn't elude him forever. Without being told, Lex reached the conclusion that his former best friend secretly hailed from Krypton in the season 7 finale prior to the two having their long-awaited showdown in the season 7 finale. Here's every moment that helps explain Lex's game-changing realization.
6 Clark Saved Lex From Drowning
Lex's suspicions were rooted in the series premiere when Clark rescued Lex from the crash on the bridge. Clark originally chalked this up to "adrenaline," but Lex had a difficult time buying into this notion. As evidenced by the secret room in the Luthor Mansion dedicated to the events that took place that day, Michael Rosenbaum's Lex was convinced that there had to be a special reason Clark was able to free Lex from his car and pull him to safety. All of Lex's speculations about Clark potentially having abilities came back to this incident, which effectively jump-started his obsession of the Kent family.
5 Clark's Connection To The Kawatche Caves
Many contributing factors destroyed Clark and Lex's friendship in Smallville, one of which being the former's repeated denials of having any knowledge of the Kawatche Caves. Since season 2, Lex had been of the opinion that Clark was keeping information about the Kawatche Caves to himself. Clark's unexplained interest in them and proximity to strange events occurring within the caves proved to Lex that he had to be hiding something. Clearly, Lex knew he was right when he found a map Clark had made of the caves. It was through this map that Lex's science team discovered the hidden chamber that acts as a gateway to the Fortress of Solitude.
In Smallville season 5, the series confirmed to Lex what Clark (and the viewers) already knew: the Kawatche Caves are linked to the Kryptonian race. In the premiere, he was attacked by three Kryptonians in the caves looking for "Kal-El." For Lex, this had to be one of the biggest clues, as Tom Welling's Clark being an alien would naturally explain his connection to the Kawatche Caves, which Lex knew to be a place once occupied by extraterrestrial beings. Apparently, Lex did indeed connect the dots eventually. This was made apparent in the season 7 finale when Lex called Clark "Kal-El" in reference to his confrontation with the Kryptonians in season 5.
4 Dr. Walden's Warning About Clark's Future
When they faced off in the season 7 finale, Lex described Clark as an alien "plotting our demise." This description is eerily similar to what Dr. Walden said about Clark in season 2's final episodes. After being bombarded with energy from the caves, Dr. Walden set his sights on Clark, believing that he was invader from another planet who would try to conquer the world. He even shared his thoughts with Lex, who dismissed them as delusions at the time. But by the end of Smallville season 7, there's a good chance that this incident from Clark's sophomore year served as a crucial piece of the puzzle. His warnings about Clark had to be at the forefront of Lex's mind when he learned about an alien lurking in Smallville.
3 Clark's Resurrection In Smallville Season 5
Any lingering doubts Lex had about Clark being an extraordinary individual were erased in season 5. After losing his powers, Clark died to a gunshot wound. Just minutes later, he was resurrected by Jor-El, who had briefly possessed Lionel Luthor's body. In a conversation with Lana in "Hidden," Lex used the fact that Clark came back from the dead to support his claim that Clark isn't a normal person. Kristen Kreuk's Lana couldn't refute it, and by that point in the series, it would be difficult to argue Lex's point. After all, there was no medical explanation for Clark's return.
2 Clark's Relationship With Dr. Virgil Swann
In Smallville season 7, Lex's investigation into the Veritas group yielded some major revelations. Lex learned that the secretive organization was looking for a Kryptonian who crash-landed on earth during the meteor shower. One Veritas member was Christopher Reeve's Dr. Virgil Swann. While some within the group, like the Teagues and the Queens, remained oblivious to Clark's identity, Dr. Swann was able to identify Clark as the Traveler as early as Smallville season 2. The pair had two onscreen meetings with each other, and presumably met on other occasions as well. Lex found out about their friendship in a season 4 episode when Jason Teague brought it up.
Lex was shocked to learn of Clark's connection to a reclusive, billionaire scientist, as there was no obvious reason for the two to associate with one another. One finally presented itself when Lex found out that Dr. Swann was involved in the search for the Traveler. Clark having a mysterious relationship with a scientist looking for an alien was one of the most glaring giveaways.
1 Brainiac's Big Hint
Lex received one final hint before his final showdown with the Traveler in the Smallville season 7 finale. By this point, he already knew that the Traveler was someone who'd been living in Smallville since the first meteor shower, which was a profile Clark easily fit. He asked Brainiac (disguised as Kara) who the Traveler was. The villain's response was, "don't you already know?" Brainiac didn't mention Clark's name, but saying it out loud wasn't necessary. Lex understood from that the truth had to be right under his nose, meaning that it was someone he should have suspected from the beginning.
Judging by everything that had happened to Lex in the last seven years, the only candidate that made any sense was Clark. All the clues were there; Clark's superhuman abilities, his connection to a cave with alien origins, and the link to Dr. Swann were all details that could've given Lex the answers he sought. He just hadn't pieced them all together until that very moment. Brainiac's tease in Smallville season 7 provided that last push Lex needed.