In Lost, which episode reveals that the survivors have been living in a flash-forward?

In Lost, “Through the Looking Glass” reveals that the survivors have been living in a flash-forward.

The season-three finale uses a structure that initially appears to be another flashback involving Jack Shephard. Near the end, however, Jack meets Kate in the present day, and their conversation reveals that the scenes are actually set after the island events shown in the main storyline.

This twist is one of Lost’s most notable narrative reveals. It changes the audience’s understanding of the episode and establishes flash-forwards as a major storytelling device for the following season. The finale also includes events involving the Looking Glass station and Charlie Pace.

The title is often confused with the DHARMA station itself, which is also called the Looking Glass. The episode title refers to Lewis Carroll’s Through the Looking-Glass while also matching the station’s name.