SAN FRANCISCO (Map, News) - Following the success of “The Lion, the Witch and the Wardrobe,” his movie adaptation of the C.S. Lewis classic, New Zealand-born director Andrew Adamson faced a unique hurdle in crafting its follow-up, “Prince Caspian,” which opens Friday and has a special screening Saturday at the Metreon.

Unlike the “Harry Potter” series, in which J.K. Rowling constructed a fantasy world around a mostly fixed crew, Lewis’ “Chronicles of Narnia” features an ever-changing cast, leaving Adamson to build a sequel around an unfamiliar hero: Caspian, the embattled prince destined to liberate Narnia from the tyrannical grasp of his treacherous uncle, Miraz.

Enter Ben Barnes, the dashing young “Stardust” star who sacrificed one dream — a lead in the British National Theatre’s production of “The History Boys” — to pursue another, in one of Hollywood’s most promising franchises.

For 26-year-old Barnes, a handsome London native for whom reading the Narnia books was an almost inescapable rite of passage, the decision to accept the role in “Caspian” wasn’t impossible, despite his contract with the theater.

“To me, working with the National Theatre is the pinnacle of all acting, so it was unfortunate that both my dreams came true in the same year,” he says. “That sounds like an awful, conceited thing to say — ‘Woe is me, two of my lifelong dreams came true at the same time’ — but it was difficult, because I consider myself a loyal guy. It was hard for me to leave early, but I don’t regret it.”

While “Caspian” is the first chapter of Barnes’ Narnia adventure, it represents a bittersweet swan song for “Wardrobe” co-stars William Moseley and Anna Popplewell, who play schoolchildren-turned-swashbucklers Peter and Susan Pevensie. Both actors will bid reluctant farewell to the franchise in the wake of the second film.

Yet that didn’t damper Moseley’s mischievous spirit during the shoot, when he threw orange juice all over Barnes the very first time he appeared in costume, a process that took two hours to complete.

Barnes says, “I wanted to kill him. And he just runs off — Will’s very fast, and he’s already gone. Meanwhile, I’m surrounded by all these poor people who’ve spent ages dressing me up and doing my hair, their mouths are agape.”

Moseley, 21, grins when reminded of the prank, saying only that “Caspian” required his most physically and emotionally draining work to date.

As for departing the franchise that gave birth to his career? Moseley acknowledges his reluctance to leave, but hopes to follow in the footsteps of onetime co-star James McAvoy, who used his role in “Wardrobe” as a stepping-stone to “The Last King of Scotland” and “Atonement.”

He says, “I have these nostalgic memories, of course, but I feel as if I’ve graduated from Narnia and learned what I can from these experiences, sort of like my character in the film. I don’t mean to sound ungrateful, far from it. I believe that I’ve gone to the next level as an actor, and I can’t wait to see what’s on the horizon.”

A few words from ‘Prince Caspian’ co-stars

Georgie Henley, as Lucy Pevensie, on her uncertain future: “There are so many things I want to do. I’d like to write, and I want to make music, if I ever get the opportunity. And of course I will keep acting for now because I’m very excited about our next movie, ‘The Voyage of the Dawn Treader.’ But most 12-year-olds don’t know what they want to do with the rest of their lives. I certainly don’t.”

Peter Dinklage, as Trumpkin, on his distinctive hairdo as Narnia’s most hospitable dwarf: “[I needed] a really long red beard and wig made of yak hair. Somewhere, there’s a yak on top of a mountain who’s very cold. And I’m sorry. However, we filmed during the summer in Prague, so it was not the coolest of makeups for me.”

Anna Popplewell, as Susan Pevensie, on entrusting future Narnia films to a newcomer: “Ben had a lot to live up to before we’d even met him, especially for William and me, because we knew that we were not in the next story. We were, in a sense, passing the films onto someone whom we really liked. He had that something that we connected with.”

IF YOU GO

Prince Caspian screening and luncheon, presented by C.S. Lewis Society of California

Where: Metreon, 101 Fourth St., San Francisco

When: 10 a.m. Saturday

Tickets: $20 to $50

Contact: (510) 635-6892 or www.lewissociety.org

Note: Guest speaker is Michael Ward, author of “Planet Narnia”