Brad Pitt will be in London Tuesday to begin playing Moriarty, Sherlock Holmes' nemesis, for the new film starring Robert Downey Jr. and Jude Law. reports that Guy Ritchie, who directed Pitt in Snatch, decided to add him to the cast after watching the first edit of the film.

Sherlock Holmes was due in theaters this December, but has now been pushed back to 2010.

"This is all such mad rush now, having such little time to get everything done," a source tells the magazine. "There's just a week to get this done and everyone is just praying the weather stays clear and time doesn't run out too soon."

Brad Pitt's Inglourious Basterds will begin its theater run this Friday, August 21.

Update: Warner Bros. has now denied the story. Details here.

Story by Casey Johnson contributing writer