Robert Downey Jr. has already revealed at "The Ellen DeGeneres Show" back in 2014 that "Iron Man 4" is definitely in the works. At the same time, reports also revealed that the famous Hollywood actor will reprise as a private detective in "Sherlock Holmes 3."

As the actor is clearly more prepared to be Sherlock Holmes, fans wonder if 51-year-old actor will come back in "Iron Man 4" as Tony Stark. IGN has already confirmed that Jude Law and RDJ are pairing up for the third time for Arthur Conan Doyle's film adaptation of Sherlock.

At the same time, Marvel Studio has neither confirmed nor denied the rumors regarding "Iron Man 4." Some fans theorize that Marvel Cinematic Universe may branch out to incorporate comic book plot. If the theories are indeed true, then Tony Stark (Robert Downey Jr.) will be seen mentoring a young girl, Riri Williams, in the speculated fourth installment of "Iron Man."

Since there has been no official update about the Marvel film, rumor has it that Downey may be too old to continue playing the iron clad superhero. Some even claim that the actor's asking fees is too high for MCU to pay. At $33 Million, the "Avengers: Age of Ultron" actor is one of the highest paid actors in Hollywood, Forbes reported.

Meanwhile, there is also speculations that Downey Jr. may not star in another "Iron Man" film because the studio plans to eventually kill off his character in the upcoming "Avengers: Infinity War." This will help MCU to bring in more superheroes in their films.

It is also believed that if Marvel indeed kills Tony Stark, his character will be carried on by Riri Williams, the character that Marvel introduced in its comic books last year and named her as Iron Heart.

While "Iron Man 4" is yet to be officially confirmed, fans can still see Downey Jr. Iron Man in "Spider-man: Homecoming," where Stark will be seen training Tom Holland's Peter Parker.