Robert Downey Jr has revealed 'Sherlock Holmes 3' is in development.

Speaking during a question and answer session on Reddit, the 49-year-old actor - who starred in the two earlier Sherlock Holmes films - confirmed that the third instalment in Guy Richie's series is in the works.

Asked whether there are plans in place to make another movie, Downey Jr remarked: ''Yes, we have a Sherlock 3 in development. We want it to be the best of the series, so that's a pretty tall order.''

The news follows various hints offered by other people involved in the two earlier films, the last of which was 'Sherlock Holmes: A Game of Shadows' in 2011.

Last year, for instance, Downey Jr's co-star Jude Law - who plays the role of Dr. John Watson - said he believed writing had already started on the much-anticipated third movie.

Meanwhile, Downey Jr recently suggested he will continue to play the role of Iron Man in the Marvel films.

He is contractually obliged to play the iconic character in 'Avengers: Age of Ultron' - which he's already completed filming - as well as another 'Avengers' movie.

But Downey Jr has also hinted he will continue to play the role thereafter, telling The Hollywood Reporter: ''I'm sure we'll ride that thing. You've got to surf that all the way in to shore.''

He added: ''I think I was at the forefront of something that was coming into being, and I think it has carried me as much as I have informed it.''