Actor Benedict Cumberbatch and Sophie Hunter arrive at the 72nd Golden Globe Awards in Beverly Hills
IN PHOTO: Actor Benedict Cumberbatch and Sophie Hunter arrive at the 72nd Golden Globe Awards in Beverly Hills, California January 11, 2015. Reuters/Mario Anzuoni

"Sherlock" team has begun the production on the one-off special episode, which is expected to air on Christmas, Dec. 25. Recently, Benedict Cumberbatch, who plays Sherlock, and Martin Freeman, who plays Dr Watson, were reportedly spotted filming at the Coston Hall in Bristol, England. Stephen Moffat and Mark Gatiss have written the one-off special episode.

Gatiss, co-writer of "Sherlock," posted the photo of the "Sherlock" Special clapperboard on Twitter. He posted the photo on Jan. 06, saying "Element-hairy, my dear Watson! #Sherlock." On the clapperboard, one can see Take 1, Scene 24, Roll 005, Dir., Douglas Mackinnon, DOP, Suzie Lavelle, Date, 06.01.15 written on it. Gatiss posted on Wednesday, "This is definitely a night to be inside reading 'Sherlock Holmes' not shooting it."

BBC One has dropped the biggest hint that the one off special episode, if not "Sherlock" Season 4, is scheduled to air this year. "Enjoy 2015 Trailer -- BBC One" also features some glimpses of Sherlock Holmes, who seem to be in an investigative mood, along with scenes from other shows.

The one off special episode is set to answer the question about Moriarty, whether he is still alive or is dead. In Season 3 finale, the gif of Moriarty appeared on the TV screens across the country, repeatedly asking, "Did you miss me?" Gatiss said to Radio Times that the special episode will "completely" solve Moriarty's reappearance mystery.

There is still no information on "Sherlock" Season 4 production schedule. Cumberbatch is expected to soon begin shooting for "Doctor Strange." He is playing the titular role in the film. The production on the three episodes of "Sherlock" Season 4 may begin after Cumberbatch, who recently revealed that he and his fiancée Sophie Hunter are set to become parents for the first time, wraps up his "Doctor Strange" filming.

If the filming of "Sherlock" Season 4 completes this year, it is highly possible that the new season will premiere in Jan. 2016. After "Sherlock" Season 3 finale, the writing duo Gattis and Moffat announced that they have already mapped out Season 4. The new season is said to be a dark one.

[Youtube/BBC]

Contact the Writer at a.shrivastava@IBTimes.com.au