UPDATE 7:30pm: Well, it looks like we can expect the announcement within the next couple of weeks.
Blizzard developers are set to host a Comic-Con panel on the 21st July, entitled "Behind The Scenes of Overwatch's Newest Hero".
It's unclear whether this will include the reveal itself, or if that will happen beforehand.
UPDATE 9:00am: A second tweet, this time from the Brazilian Overwatch Twitter account, suggests the game's new hero could be Ana Amari. Check the top left of this image, which shows an additional recipient for the blueprint design, not included in the other tweets.
So who is Ana Amari? Excellent question! She was one of the founding members of Overwatch, thought to have disappeared after the group originally disbanded. She also happens to be Pharah's mother.
Although some think she was killed around the same time as Jack Morrison, there is something of a precedent for characters pretending to be dead before returning under a different name and appearance. For example, Jack Morrison.
We also know she was a sniper, thanks to a brief look at the original team in Soldier 76's origin story.
The rampant speculation continues.
ORIGINAL STORY: Rumours that Overwatch's next hero will be a support sniper are looking pretty solid right now, as the game's official Twitter account teases a new image.
The tweet features a proposed blueprint for a new "prototype biotic rifle", designed by Overwatch's Torbjörn, with accompanying comments from himself and Mercy. She notes her concerns that although the rifle has been designed with medical purposes in mind, it could potentially be weaponised. Interesting!
Fans have been speculating for a while that the next hero is likely to be another sniper - like Hanzo or Widowmaker - but crucially, this character is thought to play more of a supporting role, rather than being another offensive character.
The leading theory is that the next Overwatch hero will be called Sombra, thanks to a number of hints found in the game's Dorado map. This assumption is helped somewhat by a comment made by game director Jeff Kaplan in a recent interview with Eurogamer: "I would say it's about time that people are concerned with who Sombra is."
No word yet on exactly when the next hero will be announced, but if you want to take a look at everything we know so far, here's a video we put together last month. This latest image does seem to confirm a lot of our guesswork.
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