'Sherlock' Season 4 PHOTO: Martin Freeman, Benedict Cumberbatch SPOILERS On BBC One Look!

The game is on at BBC One once more: Mark Gatiss has just shared the first teaser pic of Martin Freeman returning to his role as Dr. John Watson in Sherlock! The series, which stars Benedict Cumberbatch in the title role, began shooting a few days back. The showrunner and co-star teases photos from the set as the two main actors finally find time to film the show!

For the second time in the past few days, Gatiss has shared an obscure but obvious photo of one of the Sherlock stars on Twitter; following up his snap of the back of Cumberbatch's head last week, the man who plays Mycroft Holmes now shared a similar pic of the back of Freeman's head.

Back 2. #Sherlock pic.twitter.com/iRAHPm5kDC

— Mark Gatiss (@Markgatiss) April 13, 2016

These are so far the first two proofs that production is gearing up. While there was a one-off special in January, it's been nearly two years since fans have seen a new season of Sherlock. By the end of season 3, it appeared that Jim Moriarty (Andrew Scott) had come back from the grave, but the "Abominable Bride" special hinted that there had to be something more to it than that, since it was clear he had died by the end of season 2.

Since Sherlock began in 2010, its two main actors have turned into Hollywood superstars. Freeman went on to play Bilbo Baggins in Peter Jackson's Hobbit trilogy and the lead role in FX's Fargo, while Cumberbatch has seemingly been everywhere in the past few years: from sci-fi villain in Star Trek: Into Darkness to Oscar nominee to Marvel superhero in the upcoming Doctor Strange.

Freeman will also be part of the Marvel Cinematic Universe starting in a few weeks: the actor is part of the cast of Captain America: Civil War in the role of Everett K. Ross, which he will reprise in 2018's Black Panther.

It's unclear when the BBC will air season 4 of Sherlock.