Mark Ruffalo entered the MCU in the first Avengers movie, unlike the rest of the heroes in that film. Even Black Widow and Hawkeye had their place in the MCU prior to the Avengers dropping. Ruffalo was late to the scene, but he was the final piece to the puzzle. He brought a new depth to the tortured scientists Bruce Banner, and Marvel fans flocked to his character. 

Over the years, Ruffalo has slipped spoilers about the MCU to the public. In fact, he spoiled the ending of Infinity War in an interview alongside Don Cheadle. When the Hulk actor graced the set of The Tonight Show with Jimmy Fallon last week, he trolled fans with a title reveal for Avengers 4. Tweeting at Fallon prior to the episode airing, Ruffalo hinted that he dropped a spoiler during the interview. The obvious joke was received well by fans, who tuned in just to get any hint at what the title may be. Instead, Ruffalo's words were edited out, leaving viewers at a loss. 

One fan took that edited audio and screened it, because, why not?  Anton Volkov was able to sift through the edit and discern what Ruffalo said. The actor can clearly be heard saying "The Last Avenger." While it seems very unlikely that Ruffalo told a room full of people the real title, it can be a very important hint. Captain America's first solo film was called The First Avenger, and coming full circle to reference the Last Avenger makes sense for Disney. It sounds similar to their The Last Jedi approach as well, which ended with a main character dying. Captain America actor Chris Evan did just complete his scenes for the film, marking the end of his contract with Disney and Marvel. Will The Last Avenger really be the title?