A teaser trailer for the film has been released on Twitter, saying: "Every generation has a legend."
The announcement was made at a Star Wars celebration event being held in Chicago.
The JJ Abrams-directed film will be released December 20.
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Abrams has said Carrie Fisher's Leia will live on in Star Wars: Episode IX which has been called Star Wars: The Rise Of Skywalker.
The director said he was able to integrate unused scenes of Leia from The Force Awakens into the story.
Speaking at the Star Wars Celebration event in Chicago, Abrams said having a CG character, recasting or just having her disappear were not options.
Fisher died in December 2016, after shooting had finished on The Last Jedi, and her character is alive in the last shot of the film.
It has been a lingering question as to how the final instalment in the new trilogy would handle Fisher's passing.
Abrams said that Leia lives in the film in a way that is mindblowing to him.
The director also said Star Wars Episode IX does not pick up immediately after the events of The Last Jedi.
He said some time has gone by since the events of the last film and teased that it will be an adventure that the group goes on together.
Lucasfilm president Kathleen Kennedy also reiterated that Episode IX will close out the newest trilogy and the nine-film Skywalker saga that began in 1977.