Speculations claiming that Robert Downey Jr. will no longer star in the fourth solo "Iron Man" movie have become more and more persistent as it is widely believed that Marvel Cinematic Universe (MCU) will be ushering in a younger actor to be the next iron-clad superhero in the movies.

Rumors on Downey Jr. no longer top-billing "Iron Man 4" have been around for quite some time already. While there are those who suspect that the reason he no longer wants to star in another solo "Iron Man" movie is that he may be old for the role already, there have also been claims that he and Marvel do not see eye-to-eye on how much his talent fee should be.

After Time reported back in July that Marvel was introducing Riri Williams, a 15-year-old Afro-American girl, as the new iron-clad superhero, speculations saying that Downey Jr. will be replaced in the movies have resurfaced. In fact, it is even suspected that Downey Jr.'s Tony Stark/Iron Man character will be killed off in next year's "Spider-Man: Homecoming" so that MCU can officially usher in Riri Williams as the new iron-clad superhero, who is now known as Ironheart.

However, apart from the Riri Williams, there are also speculations that Marvel is actually waiting for Ty Simpkins, the child actor in "Iron Man 3" who served as Tony Stark's sidekick, to grow up and make him the new Iron Man. As Simpkins is only 15 years old, it is said that Marvel is releasing the "Iron Man" movie in 2019 so that the actor will be old enough to portray the role.

Whether it's Simpkins or Riri Williams (and whoever plays the role), one thing is common between the two rumors: Downey Jr. will be replaced by somebody younger. 

Back in March, Downey Jr. already confirmed in an interview that there is no plan for an "Iron Man 4" movie, and that "Captain America: Civil War" was already his "Iron Man 4" movie of sort.

"In a way, it's Cap 3, but for me it's like my little 'Iron Man 4' and then, it's back to the thing we all recognize. Everything pulls over to the side of the road when the thunder of an Avengers thing comes through because that's how it is until it changes. If it changes," Downey said in an interview with USA Today back then.

Is MCU really ushering in a new Iron Man in the movies? Fans can only wait and see.