SDCC: SHERLOCK Series 4 Teaser - And A New Holmes Brother?

And Moffat assures us that the fourth series is probably not the last.

Sherlock was represented in Hall H today, with creators Mark Gatiss and Steven Moffat, Executive Producer Sue Vertue and stars Benedict Cumberbatch and Amanda Abbington in attendance. (Martin Freeman was back in the U.K., filming a scene for the show. "He's the only one of us actually working," Cumberbatch said.) They opened and closed the panel with a look at a Series 4 trailer, which feels a little uncharacteristically action-packed: 

It's always great to see that terrifying weirdo Moriarty (Andrew Scott), and Toby Jones is a welcome villainous addition, as well. 

Some potential big news! Every other year, Gatiss and Moffat reveal three keywords about the upcoming series, and this year those words were proper nouns: Thatcher, Smith and Sherrinford. Sherrinford must refer to Sherrinford Holmes, the "hypothetical" elder brother to Sherlock and Mycroft. A little more about Sherrinford:

He was first proposed by William S. Baring-Gould who wrote in his biography "Sherlock Holmes of Baker Street" that Sherrinford was the eldest brother of Sherlock Holmes. Holmes once stated that his family were country squires, which means that the eldest brother would have to stay to manage the house. If Mycroft were the eldest then he couldn't play the role he does in four stories of the Sherlock Holmes canon, so Sherrinford frees them both. This position is strengthened by the fact that Mycroft's general position as a senior civil servant was a common choice among the younger sons of the gentry.

A little more scoop from the panel: 

Series 4 will be "the darkest yet," teased Gatiss, and Cumberbatch agreed, "It's an emotional roller coaster. With great jokes!" 

When discussing the ways Sherlock has grown and changed since the first series, Moffat said, "You can't have a show about a genius who doesn't learn. He can't be the same weird, cold, amoral man we met in Series 1, because then he's not learning. And geniuses do learn."

Although Moffat insisted he would reveal "absolutely NOTHING" about Series 4, we did learn that they're two weeks from finishing production on the fourth series, and that despite rumors, they've "never said Series 4 would be the last. We love the show and would love to keep doing it."

And lastly, in a fun little video filmed by the cast and crew for the SDCC audience, we see Gatiss and Moffat talking in front of a wall with sticky note ideas for the upcoming series. One note says "A Doctor Who/Sherlock spinoff?" and underneath, in Moffat's writing, "Over my dead body." So that answers that!