Mark was introduced to viewers in season 2 of the show. He was Derek Shepherd’s childhood friend. The two, however, went separate ways after Mark slept with Derek’s ex-wife Addison Montgomery ...

Mark Sloan, also known as McSteamy, was part of the reason why Derek Shepherd left Addison. After Sloan slept with Addison, he decided to follow her to Seattle Grace Hospital to win her back.

Richard: How are you gonna do it? Derek: I don't know. I just decided. Owen: Morning. Sir. Mark: Shepherd's proposing. Owen: Congratulations. That's a big step. Mark: It's dangerous. People who ...

The flashback episode explains how Meredith, Derek, Cristina, Arizona and Mark survived the plane crash and offered more insight into how they arrived at their current emotional state.