'Sherlock' season 4 air date updates: Actor-writer Mark Gatiss describes 4th installment as 'best one' yet; new photo released

August 5 was the last day of filming for "Sherlock" season 4, which has been described as the darkest series to date in terms of villain. If the latest promotional shot for the series is anything to go by, it looks like the dynamic duo of Sherlock (Benedict Cumberbatch) and Watson (Martin Freeman) are keeping up with the upcoming installment's somber mood.

In a new photo for the upcoming season, the detective pair is shown in their typical 21st-century attire, albeit without mustaches. Nevertheless, the dark colors of their clothes and their brooding glares seem to underscore the "creepy" vibe spewed off by the entry of Toby Jones, who will play 'the worst villain' to date, Culverton Smith. Check out the photo here.

Mark Gatiss who writes for the series and also stars as the semi-villainous Mycroft Holmes (Sherlock's brother) describes the upcoming installment as the "best one" yet. He dished that they have just wrapped up production for the series and shared a few more details about "Sherlock" season 4.

"It'll be on, probably at the beginning of next year when it usually is. We're very excited about it. I think it's the best one we've done, it's very big chewy stuff, meaty. Lots of big life changing things happen in it and all kinds of non-specific things like that I can say about it," Mirror quotes him as saying during a guesting with "BBC Breakfast."

Aside from Culverton Smith, Jim Moriarty (Andrew Scott) will be back to make life even more miserable for Sherlock. There are speculations that Sherlock will die in season 4, no thanks to the machinations of Smith. If that's the case, does it mean there will no longer be a fifth season of the detective drama that fans all over the world have come to love?

In an interview with The Telegraph back in July, co-creator Steven Moffat hinted that the fourth season might be the show's last. Throughout seasons 1 through 3, the show has taken lengthy breaks to accommodate the busy schedules of the highly in demand Cumberbatch and Freeman.

"I don't know how long we can keep it going," Moffat told the publication. "I'm personally willing, but I'm hardly the main draw. I would be moderately surprised if this was the last time we ever made this show. But it absolutely could be."

"Sherlock" season 4 is set to air in early January 2017. Keep tuning in for more details about the show. In the meantime, check out the first look at season 4 below.