While we know Toby Jones will join the cast of "Sherlock" as the fourth installments villain, the production team has been tight-lipped about who the actor will be portraying until now.

According to Den of Geek (via Cultbox), an update to Jones' resume has let the secret slip that the actor will be playing the classic Holmes villain Culverton Smith. 

Smith first made his appearance in Sir Arthur Conan Doyle's "The Adventure of the Dying Detective," which was originally published back in 1913. In the story, the villain murdered his nephew and tried to murder Sherlock by using a spring-loaded box set to release an infectious disease, but Sherlock is one step ahead of him. The detective pretends to become gravely ill, drawing a confession out of Smith who believes he has killed the famous detective, only to be digging himself in a deeper hole.

This plotline sounds like it will be loads of fun to see translated on screen with the BBC's "Sherlock" and cast. The story is set in John Watson's (Martin Freeman) second year of marriage to Mary (Amanda Abbington), which will mean viewers will more than likely see Mary alive and well in the fourth season.

Meanwhile, after the news was revealed that Jones would be joining "Sherlock" as the villain, both showrunners Steven Moffat and Mark Gatiss praised the actor's accomplishments and expressed how thrilled they were with him joining. Moffat said, "Delighted to have Toby Jones on board, bringing to life one of Doyle's finest villains." With Gatiss adding, "We're thrilled to welcome one of our finest actors to the Sherlock family. I know Toby will embrace the part with true relish!"

Back in July 2014, the BBC announced that filming for "Sherlock" would begin in late 2015, however, Moffat revealed the production team was not ready to film and announced in May 2015 that filming would begin April 2016. 

As Moffat said, filming began earlier this year in April and the series is expected to air in early 2017.