"Sherlock" season 4 will have three episodes as usual, but the titles of the first two have already been announced by BBC with the third one kept secret until now.

Reliable tipster Ruther2 has leaked the title of the third episode, "The Final Problem," which is also the title of one of the most popular stories by Sir Arthur Conan Doyle.

Interestingly, this is the only episode in "Sherlock" season 4 whose title is canon, and some fans have become skeptical because of this, but it is believed to be legitimate.

This is because the nature of the episode title itself would give away what the episode has in store. However, some fans still think it is no more than a red herring.

"The Final Problem" actually chronicles the ultimate showdown between Sherlock (Benedict Cumberbatch) and his rival James Moriarty (Andrew Scott).

This is also the story where Doyle killed off Sherlock in the hopes of moving forward to his career only to be persuaded by fans for him to write more about the character.

If the "Sherlock" season 4 finale will be based on the story, this means that Scott will be back as Moriarty, as previously speculated. This might also mark the end for Sherlock and his nemesis.

This would explain why Cumberbatch recently said that "Sherlock" season 4 feels like the end of the series during his interview with GQ Magazine.

"It goes to a place where it will be pretty hard to follow on immediately. We never say never on the show. I'd love to revisit it, I'd love to keep revisiting it, I stand by that," the actor said.

"But in the immediate future we all have things that we want to crack on with and we've made something very complete as it is, so I think we'll just wait and see. The idea of never playing him again is really galling," he went on to say.

Whether or not "Sherlock" season 4 will indeed be titled "The Final Problem" remains to be seen until BBC makes it official.

"Sherlock" season 4 will premiere on Sunday, Jan. 1, 2017 on BBC.