Smallville :

A mysterious woman, Rachel Dunlevy, visits the Kents and claims to be Clark's mother. Dunleavy kidnaps Lex and threatens to kill him if Lionel doesn't reveal the truth about Clark's adoption. Lana finds her biological father, Henry Small, and confronts him, only to find out that he is not interested in her.

Clark's family finally tells Clark what happened after they discovered him in the cornfield that fateful day. Clark learns why his father hates the Luthors, how his adoption was arranged and who else has rescued Lex from death.