<P> Season three revealed why Lex endured Lionel 's harsh parenting ; his father blames him for his younger brother Julian Luthor 's death , however , Lex took the blame to protect the true killer , his mentally unwell mother Lillian Luthor ( Alisen Down ) , from Lionel 's wraith . Also , Lex 's curiosity into the symbols ( and Clark ) leads to a blowout between the two . When Lionel gives Clark a key to a room in the Luthor Mansion where Lex has been collecting information on Clark 's family , Clark informs Lex that their friendship `` is over '' . In season four , Lex replaces his father as LuthorCorp 's CEO and turns his attention turns toward finding three ancient stones , which contain the same symbols as those in the cave and on the disc . He fails to find all three stones but suspects that Clark did , and used the stones to find the treasure of knowledge they were supposed to have led to , often having confrontations with Jason Teague ( Jensen Ackles ) . Around this time , Lex 's lifestyle of bedding women and then leaving them the next day would catch up to him when one ( Cobie Smulders ) that he had previously slept with attempts to kill him . </P>
<P> Season three revealed why Lex endured Lionel 's harsh parenting ; his father blames him for his younger brother Julian Luthor 's death , however , Lex took the blame to protect the true killer , his mentally unwell mother Lillian Luthor ( Alisen Down ) , from Lionel 's wraith . Also , Lex 's curiosity into the symbols ( and Clark ) leads to a blowout between the two . When Lionel gives Clark a key to a room in the Luthor Mansion where Lex has been collecting information on Clark 's family , Clark informs Lex that their friendship `` is over '' . In season four , Lex replaces his father as LuthorCorp 's CEO and turns his attention turns toward finding three ancient stones , which contain the same symbols as those in the cave and on the disc . He fails to find all three stones but suspects that Clark did , and used the stones to find the treasure of knowledge they were supposed to have led to , often having confrontations with Jason Teague ( Jensen Ackles ) . Around this time , Lex 's lifestyle of bedding women and then leaving them the next day would catch up to him when one ( Cobie Smulders ) that he had previously slept with attempts to kill him . </P>
smallville when do lex and clark become enemies
smallville when do lex and clark become enemies
Season three
Season three