PARTING is such sweet sorrow, especially when you are saying cheerio to a $2.5 billion film franchise that has kept lots of people in work for years and generated armies of fans.

Just ask Kellan Lutz and Nikki Reed, who play Emmett and Rosalie, two of the Cullen vampire clan in The Twilight Saga series.

"I honestly didn't expect to feel this sad," says Reed. "It came by fast," adds Lutz.

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The two were in Glasgow recently for a signing event at the Buchanan Galleries ahead of the forthcoming release of the fifth and final film - Breaking Dawn Part 2. Thousands of "Twihards", as the fans are known, turned out toting posters and Stephanie Meyer's books.

To date, Meyer's saga, started at her kitchen table, has sold almost 120 million copies globally. Most things about the Twilight franchise involve big numbers, the films most of all. The first, in 2008, was made for $37 million and made a worldwide gross of $393 million. By the time of Breaking Dawn Part 1, the production budget was $110 million, with earnings of $705 million. While it is not quite Harry Potter territory – that franchise has made almost $8 billion – it is a seriously impressive box office haul.

Which is why reminding Lutz and Reed that it is all over soon makes one feel like the bad fairy at the christening. Lutz, who has just seen the final movie in New York, confesses it "hit him in the gut" to realise what he had been part of.

Reed has also been surprised by her reaction. "To make it this far I feel like we should feel nothing but extreme joy and instead I'm feeling all of these other emotions. It's not fear, or like I'm not excited about the future. It's just that this has been such a phenomenal experience, and we've been so used to returning to it and stepping back into our characters, going back to set, working with new directors. I don't know what it's going to be like not having it."

Reed, 24, and Lutz, 27, served the usual apprenticeships in television and other films before Twilight arrived. Lutz had left a degree in chemical engineering to try acting, while Reed did not finish high school.

Lutz, one of a family of eight from North Dakota, acknowledges that giving up a scholarship to college was a big deal at the time. "My mom wasn't happy at all but she raised me well and I had my feet on solid ground. If it didn't work out, I'm glad I tried. I love taking risks; that's what life is about."

Los Angeles-born Reed, perhaps because she left the school system early, has become something of an evangelist for education. Working on Twilight has allowed her to take extension courses at the University of California, Los Angeles (UCLA), and her travels with the films have been educational experiences too.

She has just written and performed a record with her husband, the guitarist Paul McDonald. It all helps, she says. "What gets you jobs is working hard and working on your craft. Next year I might not have a job. I can't ever look at anything as being a confidence-booster because I have to always remind myself that working in this business is a luxury, it's not the given."

Lutz will be in the new Tarzan film due out in 2013, and Java Heat, with Mickey Rourke. Reed will be seen in Empire State, a drama with Liam Hemsworth from The Hunger Games.

Reed's fondest Twilight memory is of the first film, directed by Catherine Hardwicke. "I remember the tone and the feeling of filming the first movie. There was such a lack of expectation and pressure. It was just a very different experience, there was an innocence to it that I think you can't recreate. I loved that feeling. Not that I haven't loved the rest, but if I had to pick."

Breaking Dawn Part 2 brings the tale to its natural conclusion, says Wyck Godfrey, one of the film's producers who has been with Twilight from the start.

"The first film is about new love, the second about loss, the third about choice, the fourth about the challenges of marriage and family, and this last film is about protecting that family."

Godfrey's summation hints at one of the remarkable things about the Twilight saga. For all the strange magic, vampires and bloodlust at work, it is, at heart, a modern morality tale. The Cullens believe in family and loyalty, while Bella and Edward (Kristen Stewart and Robert Pattinson) are a Goth Romeo and Juliet, devoted to each other. Just to confirm the wholesomeness, Bella is a vegetarian vampire.

No wonder many parents have been delighted for their sons and daughters to read the books, see the films and to hold Bella/Stewart up as a heroine or treat Edward/Robert as the new Elvis. Such devotion has its downside, though, as seen by the recent fan backlash on the internet against Stewart, then Pattinson's girlfriend, after she was photographed with someone else.

The last two films were directed simultaneously by Bill Condon, who won an Oscar for his Gods and Monsters screenplay and whose cv also includes Dreamgirls and Kinsey. There were two bases, in Louisiana, USA, and Vancouver, Canada. To end the series in suitably spectacular style, a large cast was called for, which required some major, near military, logistics. There was a "vamp camp" to process the vampires through make-up, and as well as 32 trailers, a tented city grew up that was so big signs such as "Cullen Avenue" and "The Yellow Brick Road" were hung up so people could find their way around.

Also saying goodbye for the last time is the screenwriter Melissa Rosenberg, another long term member of the Twilight family. Besides everything else, she thinks the films have done their bit to break a glass ceiling in the movie industry.

"This series has been really eye-opening for the industry in terms of audience- women are coming out in droves and they're seeing it repeatedly. You can have a female lead drive a successful movie. Women can make a number one box office, multi-billion-dollar franchise."

If everyone is so sorry to be saying goodbye, why not carry on? Well, there are no more novel-length books for a start. Or at least not yet. Meyer, who has spent 10 years of her life on Twilight, drops a teasing hint, however. "I wrote Breaking Dawn to be a stopping point, because I knew I was getting burned out, but I'm not sure as to whether I will put these characters away forever."

That would delight, among many others, Lutz and Reed. "I'd love to work with everyone again," says Lutz. "The only problem with that is there's ageing issues," laughs Reed. "I think we're all supposed to be 23 forever."

Lutz is undeterred, however. "We'll Benjamin Button it," he says, referring to the special effects that took Brad Pitt from an old man to a baby in David Fincher's 2008 fantasy drama.

Who knows? Weirder things have been known to happen in the Twilight saga zone.

Breaking Dawn Part 2 opens on November 16