In which episode did Debbie find out about Dexter's brother?

Question

In the show Dexter, season 6 episode 4, when Dexter Morgen walks into the crime scene with the two corpse horsemen, Dexter says "this spectacle makes me think of..." and Debbie finishes the sentence "your brother... Rudy, the Ice Truck killer...".

When exactly did Debbie find this out, as I don't remember any reference prior to this where Dexter has specifically stated that Rudy was his brother?

Answer 1

This happened at the end of Season 4 (The Getaway):

Debra finds out the truth about Dexter's mother, and tells him that she knows that Dexter's brother was the Ice Truck Killer.

Dexter pretended this news was new to him and acted surprised. He is now concerned that Debra is getting closer to finding the truth about him, which gives him more of a reason to change his life.