Jude Law will star alongside Robert Downey Jr in the film
Jude Law will be Dr Watson to Robert Downey Jr's Sherlock Holmes in Guy Ritchie's reworking of the super sleuth, the director has announced.
Ritchie, whose last film RocknRolla topped the UK box office, announced the casting at a London press conference.
Other stars confirmed include Rachel McAdams as Irene Adler, Mark Strong as villain Blackwood, and Kelly Reilly as Watson's love interest Mary.
Due out in October 2009, it will rival a Holmes comedy with Sacha Baron Cohen.
Ritchie and producer Joel Silver revealed the film will be shot in London for three months, at locations including St Paul's Cathedral and Freemasons' Hall.
The film-maker said of his new venture: "I'd like to bring something new to this project - I have a few tricks up my sleeve. It won't be a traditional Guy Ritchie thing, it will be a new Guy Ritchie thing."
Downey Jr pictured with his wife Susan
He said the film, which has the biggest budget he has ever worked with, would be an adventure movie - but refused to reveal if Holmes and Watson will wear traditional tweed and deerstalkers.
Iron Man star Downey Jnr was introduced to the project - given the working title Sherlock Holmes - through his wife Susan, who works for Silver.
The Hollywood star said: "I think me and Guy are well-suited to working together.
"The more I look into the books, the more fantastic it becomes. Holmes is such a weirdo," he added.
The film is based on the stories by Sir Arthur Conan Doyle.
The Sherlock Holmes comedy being produced by Columbia Pictures, meanwhile, will star Will Ferrell alongside Baron Cohen.
Silver said he did not fear competition from the other movie as his is coming out earlier and is an action flick as opposed to a comedy.
Law was unable to attend the press conference in London due to a longstanding engagement.