Robert Downey Jr. has had to opt out of DreamWorks’ sci-fi western Cowboys & Aliens in order to clear his schedule for a sequel to Guy Ritchie‘s enormously successful Sherlock Holmes. Both movies begin filming this summer, and since Downey Jr. is unable to do both, DreamWorks is currently looking for a replacement actor for the alien-themed western, which will be helmed by Iron Man 2 director Jon Favreau. Meanwhile, although a script has already been penned for the Holmes sequel, Warner Bros. is now racing to get the movie greenlit. It’s been rumored that they’re considering Brad Pitt to play the villain, and though a director has not yet been confirmed, they’re hoping to get Ritchie back on board for the sequel. ~Alexandra Heilbron