"Sherlock" fans have been kept in waiting for the series' fourth season, which up to now still has no confirmed release date. However, fans will catch their favorite characters once the show airs its holiday special episode in January 2016.

Based on the recent trailer of the upcoming special episode titled "The Abominable Bride," the favorite duo Sherlock (Benedict Cumberbatch) and John Watson (Martin Freeman) were seen to be in late 1800's fashion in London.

Speculations are rife that the episode will feature a time travel theme. However, Steven Moffat, "Sherlock's" executive producer, made it clear that the special episode has nothing to do with the main series, Christian Post reported.

When "Sherlock" returns for its fourth season, the show will continue bringing modern-setting episodes, the report continued.

Meanwhile, not much has been shared about "Sherlock" season 4, especially its release date. Fans have been waiting patiently, since the last time they saw their favorite characters was still in 2014.

However, it was earlier revealed by Digital Spy that the production team will start filming in spring 2016, which likely suggests that the series will return the following year.

In the same report, Moffat also shared some bits about season 4 that fans should look forward to. For instance, he revealed that season 4 will be captivating enough that fans would want more from another season.

Season 4 is also expected to feature darker episodes and is expected to reach a whole new level.

"We're going to try to take it somewhere we've never been before — and I don't mean outer space. It will be challenging place to go," Moffat told EW.

He also told Digital Spy that the next season will be "dark in some ways" and that "there's a sense of things coming back to bite you."

With those promises from the executive producer, fans should think that the return of "Sherlock" will be worth the wait.

The special episode of "Sherlock" will air on Friday, Jan. 1, 2016, at 9 p.m. EST on BBC One and PBS.