SINGAPORE (AP) — A "Downton Abbey" movie is in the works, with production likely to begin in 2018, an NBCUniversal executive said Wednesday.

Michael Edelstein, president at NBCUniversal International Studios, said it hopes to assemble 20 cast members from the popular TV series.

"There's a movie in the works. It's been in the works for some time," Edelstein said in Singapore at a red-carpet event for "Downton Abbey: The Exhibition," which features costumes, locations and never-before-seen footage from the TV show. The exhibition opened in the city-state last week and ends July 31.

"We are working on getting the script right and then we've got to figure out how to get the (cast) together. Because as you know, people go on and do other things. But we're hopeful to make a movie sometime next year," Edelstein said.

Cast members at the exhibition said they were not aware of the movie. "Oh, well, you've got confirmation before us. We have no idea if that's happening," said Sophie McShera, who played assistant cook Daisy Mason. "But we would all love to be part of the film if it was to happen, for sure."

Laura Carmichael, who played Lady Edith Crawley in the series, quipped: "Well, tell my agent, because we're still waiting to know. We're hoping that will happen soon."

Emmy-winning writer and creator Julian Fellowes also said he hoped a film would be made. "I think we've got a film in us. I hope it happens," he said.

"Downton Abbey," which concluded in 2015, portrays the lives of the aristocratic Crawley family in England and their servants amid the backdrop of such historical events as the sinking of the Titanic and World War I. It has become one of the most popular TV shows in the world, airing in at least 150 countries.

Fans lined the red carpet at Singapore's Marina Bay Sands on Wednesday to catch a glimpse of the stars. Student Jessica Nobleza, 15, held up a sign that read, "You helped us pass history."

"When I got into the show, it was kind of exam period. And season one and two involves World War I, and how it affected the whole era," she explained.

The "Downton Abbey" exhibition is to travel to the U.S. and Australia at a later date.