'Sherlock' season 4 release date, spoilers: Premiere date announced, Moriarty return and Sherrinford arrival happening?

"Sherlock" fans will welcome the new year with an extra bang as season 4 of the hit Benedict Cumberbatch-led drama will premiere on Sunday, Jan. 1 on BBC.

The announcement was made along with a new "Sherlock" season 4 trailer, which teases that "it's not a game anymore" and highlights the possible return of James Moriarty (Andrew Scott).

As revealed before, "Sherlock" season 4 will premiere with the episode "The Six Thatchers." It is expected to involve British Prime Minister Margaret Thatcher, who was mentioned in the second season of the series.

It is unclear how she will come into play in "Sherlock" season 4. The last time the show referred to her was in the form of her nickname Maggie being the password for project H.O.U.N.D.

The name Thatcher was one of the "Sherlock" season 4 clues that the cast and crew of show revealed at the San Diego Comic-Con a few months back.

The other two were Smith and Sherrinford. The former is believed to refer to Culverton Smith, a villainous character in the short story "The Adventures of the Dying Detective" by Sir Arthur Conan Doyle.

The last clue refers to the third Holmes brother—Sherrinford. The character is not exactly canon, but his arrival was teased in the third season although no name drop happened.

Sherrinford was introduced as the eldest and the brightest Holmes brother in a fictional Sherlock biography written by William S. Baring-Gould.

Sherrinford is expected to turn up in "Sherlock" season 4 or at least be a strong presence in the season. Rumor has it that Tom Hiddleston will play the part although that is not confirmed yet.

"Sherlock" season 4 will be the darkest season of the show. It will also mark the return of "ghosts of the past," which convinces many of Moriarty's return.

"This is the story we've been telling from the beginning and it's about to reach its climax," executive producer and writer Mark Gatiss revealed.