Stargate Atlantis, Season 5

Dr. McKay:
I know you'll probably think this sounds ridiculous, but a...little while ago we accidentally opened a rift in space-time. Went through to an alternate version of reality, very similar to ours in many ways. Met a team much like the one I work with, only you were the leader. You were a hero...saved the world several times over.

Detective Sheppard:
Doesn't sound much like me.

Dr. McKay:
I don't think there's much difference between you and that other John Sheppard I met. It's amazing how one incident can entirely alter the course of your life. Still...I like to believe you have the same strength of character. That's why I told you the truth.