Ever since Robert Downey Jr. said that he would be willing to do one more "Iron Man" film, fans have been speculating that a fourth installment is already in the works. It is also speculated that "Iron Man 4" will have a theatrical release in 2020.

The full line-up of the Marvel Cinematic Universe will have a total of 10 superhero films and will occupy several dates until 2019. "Captain America: Civil War," is already released, while "Doctor Strange" is scheduled for November. Marvel plans to release "Guardians of the Galaxy Vol. 2" in May 2017, "Spider-Man: Homecoming" in July 2017 and "Thor: Ragnarok," in November 2017.

When February 2018 comes, it will be "Black Panther's" time to take the limelight, followed by "Avengers: Infinity War -- Part 1" in May. "Ant-Man and the Wasp" and "Captain Marvel" have no planned dates yet, but they are scheduled for the same year.  Lastly, "Avengers: Infinity War — Part 2" arrives in May 2019. These conclude phase 3 of the MCU. Iron Man is included in several of these films, which will keep him busy.   

For the fourth film in the "Iron Man" series, the plot is rumored to be involing another member of the Avengers team that will wear an iron suit and it is going to be Natasha Romanoff (Scarlett Johansson), a.k.a. the Black Widow, Master Herald reported.

Many see its plot as strange but the theory is based on the "Ultimate Marvel" comic books series. Stark and Romanoff are in a romantic relationship, and the billionaire scientist creates a black version of the iron suit for the love of his life. Unfortunately, their relationship turns sour and they separate, but Black Widow keeps the iron suit.

It was also reported earlier that Downey wants Mel Gibson to direct "Iron Man 4," according to "Iron Man 3" director Shane Black.

"Iron Man 4" is speculated to be release around 2020, but Marvel Studios has not stated anything official about the highly anticipated movie.