Robert Downey, Jr. In 'Sherlock Holmes 2': Wearing Makeup, Dress (VIDEO)

Sherlock Holmes' greatest mystery: why is Robert Downey, Jr. dressed in drag?

Entertainment Tonight visited the set of the sequel of the hit film, 'Sherlock Holmes,' finding Downey, Jr. and co-star Jude Law in the midst of action, and in Downey, Jr.'s case, in the midst of cross dressing.

It's all part of Sherlock's new array of disguises -- and one that the star himself suggested.

"I'll just speak for myself, because I might be the exception in this," Downey, Jr. says. "I have really humbled myself in the face of trying to do this again correctly."

Later in the video, Downey takes his shirt off, making for a complete transformation.