Ever since the 2013 release of the third installment in the "Iron Man" series, fans have been anticipating a fourth movie. Fans, however, have been consistently disappointed by Robert Downey Jr.'s constant denial of another "Iron Man" movie involvement in past years.

That changes now. In an interview with ABC's "Nightline," Downey Jr. hinted that he's still willing to do another Marvel movie as the eccentric billionaire Tony Stark. He even went so far as to say that he feels like he can do another "Iron Man" movie. With this, a lot fans are excited to hear if this Oscar-nominated actor has resumed talks with Marvel.

After all, the incentives for this movie could still be lucrative. According to Deadline, the first three movies were able to get a total of $2.4 billion worldwide, with the third movie accounting for a half of these profits. With all this, it's possible for to have the fourth movie kickstarted without any problems.

Regardless, with no official announcement from Marvel, the "Iron Man 4" movie will still remain to be a rumor. Also, if ever this movie is to be released, it will most likely be after the wrap-up of the Marvel Cinematic Universe's third phase, which will be around 2020. This is the earliest estimate, since Marvel has already announced its plans for until 2019, according to Design &  Trend.

Speaking of rumors, it's also possible that the fourth movie won't even be about Tony Stark anymore. According to the Master Herald, it's possible that Natasha Romanoff, also known as the Black Widow, will wear the Iron Man Suit in this movie. The theory comes from the "Ultimate" line of Marvel comic books. In the story, Tony Stark gave Natasha her very own Iron Man suit as a gift when they were still dating. However, it turns out for the worse as the relationship deteriorated and Natasha was discovered to be a traitor.

Regardless, fans are still excited about a sequel but would still want Downey Jr.'s Tony Stark as the main character regardless.