Then, while most fans were getting excited for the forthcoming Avengers films, Robert Downey Jr. revealed that he had been in regular communication with Guy Ritchie about making a third film and that it was actually happening.
Sherlock Holmes: A Game of Shadows came out back in 2011 and, while the film certainly left itself open for a sequel, no movement on such a film seemed to be actually happening.
While some time has passed since then, it was clear the project was quite real, and now the movie even has a release date, Christmas 2020.