Those eagerly waiting for the BBC's "Sherlock" season 4 finally have some details about when they can expect the show to return.

"Sherlock" season 4 will be returning in 2016, following the show's two year gap trend seen thus far. But there's some other goodness on its way, as the BBC also confirmed that there will be a one off special before "Sherlock" season 4.

Two weeks ago Martin Freeman, who plays Dr. Watson, was the first to hint at a one-episode special while on Alan Carr's Channel 4 talk show "Chatty Man." "Mark Gatiss may beat me up, but there is an idea for this one-off special that's such a good idea," said the actor. "As I was listening to it, I thought 'we've just got to do this.' It's a fantastic, really mouth-watering idea. But I really don't know when we are going to get to do it."

Here are six known details about "Sherlock" one-episode Christmas special. The filming of the special episode will commence in January 2015 and production of Season 4 will follow. It is safe to assume the one-episode special will air on Christmas Day (or around the holiday) in 2015.

Filming for the series has been difficult as Benedict Cumberbatch and Martin Freeman both have incredibly busy schedules. "It's very hard to get together," Martin Freeman told Digital Spy. "But it's one of those things where you have to at some point just go, 'We're going to do it now' - otherwise we could be having this conversation in three years."

Moffat and Gatiss stepped onto the red carpet for the BAFTA Television Awards this week, and were asked by the Radio Times if they were any closer to fixing a date for the start of season 4′s production. The answer, according to Gatiss, is yes.

"I can officially tell you that we are moving closer to agreeing some dates to shoot. If that sounds like a party line, it is. That is proper progress because Ben and Martin and Steven are so busy, but actually trying to get everybody to interlock is... we have made significant progress."

While nothing is confirmed, rumor has it that the one-episode special will be based on the story of "The Adventure of the Blue Carbuncle."

The last scene of season 3 of "Sherlock" left fans shocked, as Moriarty seemed to be alive. Many questions were raised from this one scene, but one thing is for sure: The show will have to answer the Moriarty mystery, or at the very least, address it.

 Mary Morstan is pregnant (incredibly pregnant) which means we will likely see Watson as a new father, or a Morstan ready to pop. How a child will play into the trio's evolving dynamic will be interesting to see.

 Rumor has it that Tom Hiddleston could play the third Holmes' brother, Sherrinford Holmes. In a Q&A in Brazil, "Sherlock" co-creator Mark Gatiss, who also happens to play Mycroft Holmes in the series, joked about the idea. "Tom would be wonderful in 'Sherlock,'" Gatiss says. "But he only does movies now. What can I say? I'll ask him if you like." But whether Hiddleston could join the special, if the show at all, is yet a mystery.

"Rather excitingly, Mark and I, for no particular reason, we just got out of the rain and sat at the top of the [Sherlock] production bus ... and we just started plotting out what we could do in the future," said Moffat, reports The Guardian, adding that there are no plans to make a movie since each episode is the length of a feature. "And we plotted out the whole of series four and five. So we have got plans -- but our plans don't tend to be 'Let's blow up the world or cast the most famous person in the world' they tend to be 'What exciting twists and turns can we add to this?' And I think we've got some crackers! The ideas we had that day, I thought were the best we've ever had."