A report from Radio Times reveals that actor Sacha Dhawan has been cast for "Sherlock" season 4. The report points out that his official CV has listed the show amongst his work and he has listed his character's name simply as AJ. The report does state that the complete CV has since been taken down. 

It is also further explained that while the character AJ could be anyone in the world of "Sherlock," the actor himself has had a long experience working with Mark Gatiss and Steven Moffat, the creators of "Sherlock" and "Doctor Who."

Dhawan portrayed "Doctor Who" series creator Waris Hussein for the show's 50th anniversary special which focused on exploring the origins of the series. He also had a role for "The Tractate Middoth," which was written and directed by Gatiss. 

AJ is listed solely for the premiere episode, however, and it is undetermined if he will be making another appearance for the rest of the season.

Dhawan is not the only new face for season 4 as the series' new villain is set to be played by Toby Jones, known for his roles in "Wayward Pines" and the "Captain America" movies starring Chris Evans. 

According to The Cultbox, Jones is playing Culverton Smith. Smith made his appearance in "The Adventure of the Dying Detective," written by Sherlock Holmes author and creator Arthur Conan Doyle in 1913. Culverton is a genius villain who specializes in diseases and other bio-weapons. Culverton murders his nephew and later targets Holmes.

However, Holmes tricks everyone, including his friends and allies, and states he is sick and affected by Culverton's attack. Culverton is then tricked into confessing his crime for which the police and Sherlock properly arrest him now that proof came out of his own mouth.

"Sherlock" season 4 is expected to premiere this Christmas in the U.K. and will air in January in the U.S.