'Sherlock' season 4 release date, plot spoilers: Sherlock finds Sherrinford? Is Tom Hiddleston joining upcoming installment?

Is Tom Hiddleston joining "Sherlock" season 4 as the third Holmes brother, and did the showrunners just give away the arcs for the upcoming season? What happened at the San Diego Comic-Con seemed to indicate that.

Those who have been following "Sherlock" know that its showrunners Steven Moffat, Sue Vertue, and Mark Gatiss have the habit of releasing three keywords pertaining to an upcoming season. It's their way of teasing fans with the possible arc without divulging any spoilers. During the SDCC, the showrunners kept that tradition alive, but this time, they teased names instead of words.

"Thatcher, Smith, and Sherrinford." Gamesradar tried to decipher the names, and the publication said Thatcher was the password that appeared in season 2's "The Hounds of Baskerville" episode. While it seems irrelevant at this point, it could be noted that early photos from the production of "Sherlock" season 4 showed Benedict Cumberbatch getting cozy with a dog.

The second name, Smith, is fairly common, but it's the last name that merits attention. Sherrinford is the name of Sherlock's eldest brother, the one who was left to look after the family estate.

Moffat and Gatiss have previously teased that "Sherlock" season 4 would be chock full of surprises, and the recent BBC teaser trailer showing Tom Hiddleston ("Avengers") as the third Holmes brother, Sherrinford, could be one of those surprises. The Independent reported this, as well, referencing a tweet posted on the BBC Store Twitter page.

Apparently, the tweet read, "'Blud' rumors are flying - but what could #Hiddlebatch actually look like?" Oddly enough, the tweet cannot be searched anymore, so it must have been taken down, probably to stop rumors of Hiddleston being part of "Sherlock" season 4 from circulating.

Nevertheless, some fans want to believe that Gatiss' photo with Hiddleston during the SDCC, which he captioned, "Blud. #SDDC16," is an allusion to the "Thor" actor's involvement as the third Holmes brother.

At this point, rumors of Hiddleston joining "Sherlock" season 4 should be taken with a grain of salt. Unless BBC or the actor himself confirms it, it should be taken for what it is, a rumor.

In the meantime, keep coming back for more news and updates about "Sherlock" season 4, which is slated to premiere in January 2017.