New details about the possible return of Sherlock Holmes's greatest rival James Moriarty (Andrew Scott) in "Sherlock" season 4 have emerged.

During the show's filming on St. Catherine's Island, Wales Online spotted what appears to be a Moriarty flag over the fortress. A helicopter hovered over it while some men in black climbed to the location.

It is unclear what this means for the villainous character in "Sherlock" season 4 but it certainly has fans excited as they have been waiting for the big comeback of the character.

His potential return was first hinted at when he appeared in the "Sherlock" season 3 finale, in a static image on a television screen. A voice recording of Moriarty saying "Miss me?" rang as the image flashed.

In "Sherlock," Moriarty appears to have shot himself in the second season to have the last laugh after Sherlock found him out. Before that, he had expressed his interest in suicide.

However, if Sherlock was able to fake his own death, it is likely that Moriarty could as well. It is expected that "Sherlock" season 4 would be the season for his secret to be spilled.

Sadly, the people behind "Sherlock" have been coy regarding the possible return of Moriarty in "Sherlock" season 4.

Earlier this year, creator and executive producer Steven Moffat spoke about what fans can expect in "Sherlock" season 4 with regards to Moriarty during a post-mortem interview about Last year's Christmas special, "The Abominable Bride."

"I think what we can say is we may or may not see more of Andrew Scott as Moriarty," he said. Moffat was incredibly vague with the details all throughout the interview.

"I think there's still an ongoing element that people haven't really picked up on... I think there's stuff to come," Moffat teased.

It will be a long with before fans learn the truth, seeing that "Sherlock" season 4 is not expected to premiere on BBC until January 2017.