Actor Robert Downey Jr. held a private dinner in Los Angeles last night to celebrate the success of Iron Man 3, but also to begin negotiations for The Avengers 2 and The Avengers 3. While the actor is open to returning for the Marvel Phase Two and Three sequels to 2012's Marvel's The Avengers, he does not want to return for the potential stand-alone adventure Iron Man 4.

Back in April, we reported that the actor wanted to "retire" his Tony Stark character, but he didn't leave a timetable as to when he wanted to do so. Iron Man 3 was the last movie that Robert Downey Jr. was obligated to do, under his current contract with Marvel Studios.

Bringing Robert Downey Jr. back under a new contract will likely cost Marvel a pretty penny, since he earned an estimated $50 million from the 2012 blockbuster Marvel's The Avengers, after box office bonuses and back-end compensation. According to financial analyst Doug Creutz, the actor's departure could be just as costly.

"It would be a definite negative for that particular franchise. He is Tony Stark. The other individual franchises -- Thor, Captain America, Hulk -- etc., don't have near the level of box-office potential that Iron Man does. The other way to look at it is that Iron Man would probably look more like those other franchises in terms of box-office performance without Downey."

The Avengers 2 is slated for release on May 1, 2015, and The Avengers 3 isn't expected to hit theaters until at least 2017.