The mysterious standalone Black Widow movie is starting to gain a lot of clarity. The project has added Stranger Things' David Harbour and is talking to Rachel Weisz about joining the cast as the next Marvel movie continues to take form.

Though Marvel hasn't officially confirmed the news, it is believed one of its next projects will be the long-awaited standalone Black Widow movie. Obviously this would include Scarlett Johansson, but aside from her, we don't have any news regarding the cast—until now.

According to Variety, Oscar-winning actress Rachel Weisz is reportedly in talks to join the project. The deal isn't complete yet, but there is strong interest from both sides to get it done. Unfortunately, there are no details regarding what character she could play.

On a similar note, the project has added Stranger Things and Hellboy star David Harbour per The Hollywood Reporter. Much like Weisz's case, there are no details regarding the character Harbour would portray in the movie.

The movie is expected to follow Natasha Romanoff's origin story as a trained spy and assassin for the KGB before she ultimately makes her way to SHIELD and joins the Avengers.

A leading reason why the project is in such secrecy is that Marvel has kept its post-Avengers: Endgame plans under wraps. The only project it has confirmed is Spider-Man: Far From Home, and that's only because it comes out a few months after Endgame. Besides that, it has not set a concrete roadmap for 2020 or beyond.

But somewhere in there will fall the Black Widow movie with Johansson, Harbour and Weisz as part of the cast, if all things go according to plan.