There was also hints that Sherlock has a third brother and it was elluded to during the last episode of the third season when Mycroft said, “You know what happened to the other one.” That was enough to get fans talking and the reports on the internet are placing Thor actor Tom Hiddleston as the brother.
Hiddleston played Loki in Thor and was generally a bad ass character in the movies. The odds are good that he is going to play a similar character, but only time will tell at this point. Even though most fans are wondering if Moriarty is coming back, plenty of attention will be on HIddleston and were he falls into place.
Sherlock Season 4 will come in 2017, so for right now, fans are going to have to watch older episodes to see if they can find the hints that are left showing what fans might be able to expect for the fourth season.