The well-loved British-American crime drama "Sherlock" is headed for its fourth season next year, and its avid viewers are keen to know what will be at stake for the characters in the upcoming episodes.

The TV series' lead star, Benedict Cumberbatch, however recently dropped some hints during the San Diego Comic-con that sound like bad news for "Sherlock" fans: The upcoming fourth season is possibly the last for the show.

"We'll see how this series lands. It's been great fun to come back and do it. How it will continue in the future, who knows?" Cumberbatch said when asked about the future of "Sherlock," as quoted by The Independent.

He added that a major concern for the show is the schedule of the actors.

"It's not just about what any of us want. It's about what's actually right for the show, to be honest, and that has to be judged very carefully. Think about the very limited but classic British output of certain shows, and there aren't that many of them. It's a painful thing to say, but maybe series four is it. Who knows?" Cumberbatch said.

The actor said personally he wants the show to continue because it is "too much fun doing it." He, however, said that he does not want the series to be stretched.

"This has run longer than most U.S. series. You don't want to compromise it by continually doing it, just because we could carry it on," he said.

As for the upcoming fourth season, Cumberbatch hinted that it will be so dark compared to past installments of the show. He added that "without a doubt," the next "Sherlock" episodes will be the darkest the show has ever had.

"Myopically dark. You're talking about the end of the universe darkness. You can't see in front of you and would walk into everything dark," the actor told Collider, describing how dark the next season will be.