Hugh Grant, Emma Thompson and other 'Love Actually' cast members look back at film's 20-year legacy

Nearly 20 years ago, movie audiences around the world were treated to a quirky comedy about romance, rejection, family, the holidays and the energy of London.

Today, "Love Actually" has become a holiday classic and many fans say its magic is still there. For some members of the cast, the movie's longevity doesn't come as a surprise.

"I think that we forget, time and time again, that love is all that matters. It's all that matters," Emma Thompson, who played Karen in the film, told Diane Sawyer for a special "20/20" episode.

Thompson and other members of the cast shared their hilarious memories of making the film and revealed secrets behind the script for the special, which airs Nov. 29, at 8 p.m. and streams the next day on Hulu.

The 2003 movie follows the romantic plots of several characters in nine storylines taking place in the weeks leading up to Christmas.

The characters, whose individual stories are artfully interwoven in the film, include David, played by Hugh Grant, the newly elected British prime minister who falls in love with one of his staffers; Karen, David's sister, who has her heart broken by her husband; Daniel, played by Liam Neeson, a widower who tries to help his stepson Sam win the heart of his classmate Joanna; and Mark, played by Andrew Lincoln, who comes clean about his hopeless love for his best friend's wife Juliet, played by Keira Knightley, with a now-famous scene told through a series of giant cue cards.

The cast also includes acting heavyweights Colin Firth, Bill Nighy and Alan Rickman, who died in 2016.

The idea for the movie came from writer-director Richard Curtis, who penned other hit British romantic comedies such as "Four Weddings and a Funeral," "Notting Hill" and "Bridget Jones's Diary."

Curtis told Diane Sawyer that he's been obsessed with the idea of love ever since he was a boy. He said he appreciates that "Love Actually" emphasizes how all different kinds of love can bring out the best in people.

"I think the 20 years shows what a youthful optimist I probably was when I wrote it," he said.

"I do think, you know, the way to think about life is that every day has a potential, in all its simplicity, just to be -- just to be gorgeous."

Thompson said she was immediately drawn to the script and Curtis' energy on set when they filmed in 2002.

"[Curtis] reminds us in a film that's very funny about love," she said. "All its messiness, and its unexpectedness, and then you'll find love in the weirdest places," she said.

The role of David was specifically written for Grant, who starred in several of Curtis' films.

Grant, who is known to enjoy his reputation as a contrarian, said he was happy to step into the role of Prime Minister but had one major qualm with the script -- a victory dance that David is scripted to do after pushing back against the bullying American president played by Billy Bob Thornton.

"I think he was hoping I'd get ill or something, and we'd say, 'Oh, what a shame, we'll have to lose that dancing sequence,'" Curtis recalled.

Thompson said she recalled Grant telling her at the movie's premiere, dryly, that the movie was the "most psychotic thing" they've ever been in.

Grant told Sawyer that he didn't recall that moment from the premiere, but said calling the film psychotic wasn't necessarily a bad thing.

"It's Richard on steroids, but the thing is with him, what you have to remember is when he writes about love, he means it. And that is quite rare," Grant said.

Some of Curtis' own emotional experiences also were used in one of the movie's storylines. Sarah, played by Laura Linney, is frequently rushing to a psychiatric hospital to tend to her brother who is battling mental illness, and has to abruptly end a long-awaited romantic moment with her co-worker Karl, who is played by Rodrigo Santoro.

"'Love Actually' is not just positive love," Linney told Sawyer. "It's also the repercussions of love and the responsibility of love and the heartbreak of love."

Curtis had a sister who was hospitalized for mental illness and he said Linney's performance moved him.

"So you think, 'I want to say an enormous amount through what Laura's feeling. I've got 6 minutes to do it in. How do you do that?' And then you suddenly realize that Laura can do it in 30 seconds," he said.

Linney wasn't the only person to wow the director.

Thomas Brodie-Sangster was 12 when he auditioned for the role of Sam, the lovestruck boy who has a crush on his American classmate Joanna, played by Olivia Olson. Brodie-Sangster, who has gone on to star in other TV shows and films including "The Queen's Gambit," nailed the audition and conveyed the emotional journey the character goes through, according to Curtis.

"He could act anything," he said. "I think if we'd said to him 'Do you have any experience of cannibalism?' he would have said, 'No,' but still been able to act, you know, [like] a good cannibal."

Brodie-Sangster told Sawyer he saw the movie for the first time since the premiere last Christmas and recalled the warm memories with the cast and crew.

"Liam [Neeson] treats me like his son. He was absolutely lovely to me [and] just created this environment where I was very comfortable," he said.

Brodie-Sangster said he enjoyed how good the movie was during the recent viewing. Olson, a singer living in California, told Sawyer that she also appreciates the movie's lasting popularity and was honored to play a role in the film.

"Every Christmas, I get the calls and the texts. 'Hey -- look what I'm watching.' I mean, I think it's grown so much and it's become such this, like, nostalgic piece of our holidays," Olson said. "It's so cool that I was able to be a part of that."

The film's stars are continually warmed by the love for their film.

"I am surprised just how long this film has been in everybody's hearts. I mean, it's been decades now, I can't believe I'm old enough to even say that. But I think the reason is, is that it's so human," said Martine McCutcheon, who plays Natalie, the woman who falls in love with the Prime Minister. "It expresses all these different complicated types of love that we all long for, can experience or have identified with."

"It's amazing the way it's entered the language," Bill Nighy told Sawyer. "I've had people coming up to me saying, 'It got me through my-- chemotherapy.' Or, 'It got me through my divorce.' Or, 'I watch it whenever I'm alone.'"

"It's beloved. And it's a wonderful thing to be a part of."

Curtis said he, too, is proud that the movie's message about love in the face of any situation still resonates and that it's struck a chord with people not only during the holidays, but year-round.

"I think when you get it right, films can act as a reminder of how lovely things can be, and how there are all sorts of things which we might pass by, which are, in fact, the best moments of our lives," he said.