Long time no see/Long time no speak is said when you meet someone who you haven’t seen for a long period of time.
Some Excerpts:
From TV shows, movies and novels
Lost
Ken Leung(Miles Straume) used the phrase “Long time no see” when he and Josh Holloway(Sawyer) ran into Matthew Fox(Jack Shephard) and Evangeline Lilly(Kate Austen) in season 4 [...]