'Sherlock' season 4 air date, latest news & updates: Tom Hiddleston reportedly cast; season 4 debuts Jan. 1

There are rumors that "The Night Manager" star Tom Hiddleston will appear in the long-awaited "Sherlock" season 4.

Sources say that while Hiddleston's casting has been rumored for a while now, a photo of the actor with the "Sherlock" creators from earlier this year has reignited speculation that the actor is joining his real-life buddy, "Sherlock" star Benedict Cumberbatch, in the drama's fourth season.

According to the new trailer for the upcoming season of the British-American crime drama, fans will lay their eyes on Sherlock and his trusty Dr. Watson (Martin Freeman) once again on New Year's Day 2017.

The "Sherlock" season 4 premiere episode will find the high-functioning sociopath and his faithful friend facing the return of arch nemesis Moriarty (Andrew Scott) in "The Six Thatchers." The season 4 debut is expected to introduce the new villain played by "Captain America: The Winter Soldier" actor Toby Jones, who Deadline says is portraying one of the finest villains in author Sir Arthur Conan Doyle's "Sherlock."

Meanwhile, recent comments from Cumberbatch indicate that "Sherlock" season 4 may be the show's last. This is not entirely unexpected, given that the stars of the popular series have been and will be busy filming big-budget blockbusters and that showrunner Steven Moffat is also committed to "Doctor Who." These people have been so busy, in fact, that the last episode of "Sherlock" aired almost three years ago.

In a recent interview with the U.K. edition of GQ, Cumberbatch said season 4 "feels like the end of an era" and revealed that it may be difficult to continue the series beyond this as it "goes to a place where it will be pretty hard to follow on immediately."

Nonetheless, Cumberbatch gave "Sherlock" fans a glimmer of hope, saying that he isn't discounting the possibility of reprising the role in the future.

"We never say never on the show," the actor said. "I'd love to revisit it, I'd love to keep revisiting it, I stand by that, but in the immediate future we all have things that we want to crack on with and we've made something very complete as it is, so I think we'll just wait and see. The idea of never playing him again is really galling," he added.

"Sherlock" season 4 premieres Jan. 1, 2017 on BBC One and PBS Masterpiece.