Robert Downey Jr.'s time as the billionaire playboy-turned-superhero Tony Stark could be running out as more discussions about the plot of "Iron Man 4" continue online.

One of the rumors surrounding the fourth installment of the "Iron Man" movie franchise claims that Natasha Romanova/Black Widow will take over the Iron Man armor in the next movie.

According to Movie Pilot, Marvel could opt to get inspiration for the next "Iron Man" movie from the "Ultimate Marvel" comic book series, where Natasha turned out to be a double agent for the Russian Liberators. But before her plans was revealed, Tony decided to give her an Iron Man armor of her own when the two of them were still dating.

The report speculated that this could be Marvel's way to keep Scarlett Johansson in the Marvel Cinematic Universe and give Black Widow her very own stand-alone movie outside the "Avengers" franchise.

Marvel has yet to discuss the possibility of a female Iron Man in the future, but based on a previous statement from "Iron Man 3" scriptwriter Shane Black during an interview with Uproxx, the entertainment studio is not keen on bringing a female villain in the mix.

"There was an early draft of 'Iron Man 3' where we had an inkling of a problem. Which is that we had a female character who was the villain in the draft," the scriptwriter explained in the interview. "We had finished the script and we were given a no-holds-barred memo saying that cannot stand and we've changed our minds because, after consulting, we've decided that toy won't sell as well if it's a female."

Black also revealed that Downey would like to work with Mel Gibson as the director for the next "Iron Man" movie if Marvel will confirm its development. However, both the studio and the actor-filmmaker have yet to address the speculations.