An emotional Patrick Stewart said he was "deliriously happy" to be returning to Star Trek a generation later, telling San Diego Comic-Con that "you cannot have too many franchises in a career."
Stewart will reprise his fan-favorite role as Jean-Luc Picard in CBS's "Star Trek: Picard" after almost two decades, and presented unseen footage to a packed theater at the world's biggest pop culture fan convention.
"We never know, do we, when our best moment will be -- and that is now," he said.
His voice choking, Stewart described battling overwhelming emotions when shooting the final scenes of "Star Trek: The Next Generation" years ago, and how he had felt reluctant to return to the sci-fi franchise until meeting a writing team including Pulitzer-winning author -- and now showrunner -- Michael Chabon.
The trailer revealed the surprise return of other popular characters including Data (Brent Spiner) and Seven of Nine (Jeri Ryan) who then joined the cast and producers on stage.
It showed an age-worn, soul-searching Picard living back on Earth on his vineyard, and struggling to reassimilate.
A mysterious young woman comes to him for help, before a few brief clips showing him seemingly back aboard a spaceship.
Star Trek, a multi-billion-dollar cultural phenomenon beloved by fans worldwide, turned 50 years old in 2016.
Stewart recalled how his children had explained to him what Star Trek was when he was first approached as a Shakespearean stage actor in the 1980s.
Addressing his decision to return after years of dismissing the possibility out of hand, the "X-Men" star said: "I knew that something very unusual was going to happen. I wanted to be a part of it."
"To imagine that something like this might go ahead and I wouldn't be there, would have been just too defeatist."
The panel also featured footage from the upcoming third season of "Star Trek Discovery," set a thousand years further into the future, and new light-hearted animated Trek comedy "Lower Decks" from Mike McMahan ("Rick and Morty".)
"Picard" will be released in early 2020.
Agence France-Presse