Sherlock Season 4 Air Date and Premiere: Benedict Cumberbatch Starts Filming First Episode of Hit Detective Series

BBC's "Sherlock Holmes" season four is becoming more real for fans throughout the world.

"We're ready to unleash the most shocking and surprising series of #Sherlock yet. The only thing is to expect is the unexpected..." said BBC One.

According to Deadline, actors Benedict Cumberbatch (Sherlock Holmes) and Martin Freeman (Dr. John Watson) have started filming for a Christmas special that will air before the three-episode series, which will make up the entire season 4.

"A special, plus a new series of three episodes -- it's a record-breaking run!! Of course, it's far too early to say what's coming, but we're reasonably confident that the very next thing to happen to Sherlock and John, is the very last thing you'd expect," series co-creator, writer and executive producer Steven Moffat said in a statement.

In the season three cliffhanger, villain Jim Moriarty makes an appearance on the television screens throughout Britain with one repeating line: "Did you miss me?" In the stand-alone Christmas special, Sherlock Holmes will use his detective skills to uncover whether or not Moriarty is really dead or if his reemergence is trick that is a part of a larger, more complicated plan.

According to Mark Gatiss, who worked on the script with Moffat, fans will find out everything about Moariarty's reemergence mystery in the Christmas episode.

The episode will be filmed in the Coston Hall in Bristol, England as well as other parts of the country.

"I don't know the plot but they moved a single bed into the crypt before they started filming," an insider told the Mirror. "They also brought in some other props to put round the bed. I think they are pretending the crypt is another location and aren't using Gloucester Cathedral as part of the story."

Filming for the official season 4 will start later in this year. Season 4 will premiere in 2016.