Leia leads the Resistance in Carrie Fisher's final performance as the beloved princess in the eighth installment of "Star Wars,” which debuts in theatres on December 14.
All of Fisher's scenes for “The Last Jedi” were filmed before she died of a heart attack in December 2016.
Mark Hamill, who plays Luke Skywalker, told Reuters: "She's irreplaceable. Star Wars is about great triumphs and great tragedies. I can't think of a bigger tragedy than the loss of Leia."
Writer and director Rian Johnson said he did not change Leia's story in "The Last Jedi" after her death. It will be up to the makers of 2019 film "Episode IX" to decide the ultimate fate of the character first seen as a spunky princess in the original 1977 film.
“We didn't tailor 'The Last Jedi' to be a farewell to her, but that having been said, I think there's some moments that will really mean a lot to fans. You will see more from Leia that you haven't seen before," Johnson added.
Fisher's final film appearance is expected to boost already feverish interest in the franchise, now owned by Walt Disney.
"The Last Jedi" is expected to haul in $185 million to $215 million at US and Canadian ticket windows in the first weekend of its release, which would rank as one of the biggest debuts in film history.
The cast and director provided a few details about the film's plot. John Boyega, who portrays former Stormtrooper Finn, said the movie finds Leia, now a general, leading the Resistance against the evil First Order, during a tense time in the raging battle to protect the galaxy far, far away.
"There is a lot of pressure on the Resistance and General Leia is on the front lines having to make big decisions," Boyega said. "It's a performance that requires a heartfelt approach, and she definitely had that," he added.
Oscar Isaac, who plays Resistance pilot Poe Dameron, said Leia's role in this film mirrored Fisher's life in some ways.
Isaac said: “Leia understands she's not going to be around forever and needs to pass the torch onto someone else. She wants to share as much of her wisdom as possible."
However, Fisher would not want fans to get too sentimental, Hamill said.
"I do know her well enough to say that she would want us to be laughing and even mocking her. She was irreverent, she was cynical, and bitterly funny and caustic, but she was always fun to be around," he added.