“Love Actually” Is 20! Casting Director on Most 'Tricky' Role to Cast, Alan Rickman's 'Complexity' (Exclusive)

Fiona Weir talks to PEOPLE about the 'difficult' process of casting a 'slightly unreachable' character, as well as Rickman's casting as Harry and more

The love for Love Actually is still all around.

Twenty years after the Richard Curtis-written and directed British ensemble comedy opened in theaters, PEOPLE spoke with co-casting director Fiona Weir about its lasting legacy and the process of finding the right actors to fit the many intertwining roles.

And while "no parts are ever easy" to cast, Weir says the role of Karl — the love interest of Laura Linney's character, Sarah — was especially "difficult."

"Casting Rodrigo Santoro's part was tricky because he had to be some gorgeous guy that Laura Linney's character would adore from afar and would be lovely and charming, but also slightly unreachable," she says.

In the movie, Sarah crushes on her coworker Karl but doesn't act on her feelings for "two years, seven months, three days and, I suppose, an hour and 30 minutes," in part due to being on call for her brother, who is mentally ill and in a psychiatric hospital. But Sarah and Karl eventually find a way to connect — albeit temporarily, as their love story ends rather abruptly.

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Related: 23 Things You Never Knew About 'Love Actually'

When casting Karl, "We considered all sorts of gorgeous fellows from the U.K., but eventually we thought it would be lovely to have an actor who was from elsewhere," Weir tells PEOPLE of Westworld and Lost alum Santoro, 48, who is from Brazil.

"And it was great to cast Rodrigo who, at that point, people didn't know so well, and he's just so delightful. And we thought he'd be a great and slightly different way of taking the part," she adds.

Though Sarah and Karl don't end up together in the movie, Linney's character does have a happy ending, as chronicled in the Love Actually mini-sequel released in honor of Red Nose Day in 2017.

She's still working late and fielding nonstop phone calls, of course — though her "darling" blowing up her cell isn't her brother but her loving husband, played by PEOPLE's recently named 2023 Sexiest Man Alive, Patrick Dempsey.

Related: The Stars of Love Actually, Then & Now

Sarah is inspired in part to pursue her relationship with Karl via a conversation with her boss, Harry (played by the late Alan Rickman), during a scene in which Weir praises Rickman's performance for being equally "sardonic" and "deeply compassionate."

In the movie, Harry has long been married to Karen (Emma Thompson) with whom he shares two children. But as they struggle to prioritize their relationship amid the responsibilities of work, parenthood and more, a potential workplace romance with Harry's assistant (Heike Makatsch) throws a wrench in their holiday season.

"Alan encompassed that deeply complicated man who loves his wife and family, but has somehow lost track of something in his life and gets tempted by this other girl, but still really caress about the people who work for him," Weir says. "And so we were thrilled when Alan said yes, because we knew that he would bring even more layers and complexity to the part than was already there."

As for whether Rickman, who died in January 2016 at age 69, agreed to play Harry right away, "He needed to read the script, but pretty quickly, yeah," says Weir. "He spotted what a lovely thing it would be to be part of."

Love Actually is streaming on Netflix.

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