In the Star Wars universe, they are mighty big shoes to fill.

And little-known Alden Ehrenreich​, the young actor taking over from Harrison Ford as Han Solo, has made his first official Star Wars appearance in London before shooting his standalone movie.

The 26-year-old is best known - if known at all - for Hail, Caesar! and Blue Jasmine.

He appeared at Star Wars Celebration Europe to promote a movie currently known only as Untitled Star Wars Han Solo Anthology Film.

Directors Phil Lord and Christopher Miller (21 Jump Street, The Lego Movie) will start shooting it in the United Kingdom early next year, using many of the same as crew who have also been working on Rogue One, the first standalone movie in the sci-fi saga, and Episode VIII, the next Star Wars instalment.

The Han Solo movie centres on the iconic smuggler in his early 20s.

"The story focuses on how young Han Solo became the smuggler, thief and scoundrel whom Luke Skywalker and Obi-Wan Kenobi first encountered in the cantina at Mos Eisley," Disney said in a statement when announcing the movie last year.

Three thousand actors reputedly auditioned before Ehrenreich won the role through multiple auditions over six months.

He was supposedly the first actor to audition, dressing up as Solo and screen testing with Chewbacca inside the Millennium Falcon.

Speaking from London, Ehrenreich said of stepping inside the Millennium Falcon for the first time: "There's something about it that felt, like, so exciting that I think that was more exciting than it felt nerve-wracking.

"Being on the Falcon after having seen it for so long, you just kind of immediately go, alright, alright, yeah, cool."

The Los Angeles native was discovered by Steven Spielberg at age 14 in a bat mitzvah video before shooting his first two movies, Tetro and Twixt, with another legendary filmmaker in Francis Ford Coppola​. His other movies include Stoker and Beautiful Creatures.

While there was no word on the plot of the movie, Lord and Miller said they loved the character's dichotomy, describing him as both "sarcastic and optimistic," and adding that "he's a maverick, he's a scoundrel, he's clever but not smart."

At the same event, director Rian Johnson said Episode VIII would pick up exactly where the previous movie, Star Wars: Episode VII - The Force Awakens, finished.

"This is going to start right where the last one left off," he said. "It was a break from tradition ... The second film is where we zoom into the characters, getting to the heart of them and challenging them."

Johnson figured out the story as he watched such movies as Twelve O'Clock High ("it became extremely important"), Letter Never Sent, The Bridge On The River Kwai, The Dambusters, Sahara and Gunga Din.

"We would watch dailies come in from VII," he said. "It was probably really healthy creating the story based on our reactions to the footage rather than the cultural reactions. It was a unique experience."