Harrison Ford's secret advice for Alden Ehrenreich, the new Han Solo

Alden Ehrenreich stars as a young Han Solo in the upcoming Star Wars spin-off. Photo / screenshot

Harrison Ford has passed the baton to 28-year-old actor Alden Ehrenreich for a new Star Wars film about a young Han Solo – but not without giving him a few tips about the character he's played for four decades.

"Tell them I told you everything you needed to know, and that you can't tell anyone," Ford, 75, reportedly told the younger actor.

Ehrenreich has remained tight-lipped about the advice ("I gotta stick to my orders from the man himself," he has said), but according to Lucasfilm president Kathleen Kennedy he found Ford's insights "really, really helpful".

Ford has played the roguish captain of the Millennium Falcon spaceship in four Star Wars films, from the original 1977 blockbuster through to 2015 hit The Force Awakens.

Harrison Ford as Han Solo in Star Wars. Photo / supplied

According to Kennedy, Ford shared his idea of "who the character was", but stopped short of telling Ehrenreich exactly how to play the role. "It was perfect, classic Harrison," she said. "I think being who is Harrison is, there is no way he would step into the middle of this and start trying to dictate."

"What [Ford] did so beautifully for Alden was he talked a lot about what he remembered when he first read Star Wars, and what George had done with Han. Who the character was and the conversations he had for so many years with George about how that character developed," she told Entertainment Weekly.

"He gave Alden that kind of insight which was invaluable. There were several times in the course of making the movie where Alden would actually recount some of the things that Harrison had pointed out. I think that was really, really helpful to him."

The cast of Solo: A Star Wars Story. Photo / supplied

Ehrenreich, previously best known for his role in the Cohen brothers' comedy Hail, Caesar!, is joined in the forthcoming Star Wars prequel by a cast that includes Atlanta's Donald Glover and Fleabag star Phoebe Waller-Bridge.