Stephen Fry has been cast as Mycroft, Sherlock Holmes's even brighter elder brother, in the sequel to Guy Ritchie's 2009 reinvention of the classic English sleuth.

Fry revealed the news himself during an appearance on BBC 5 Live's Danny Baker Show. The next film in the series, which features Robert Downey Jr as Holmes and Jude Law as Doctor Watson, is due in cinemas next year.

"I'm playing Mycroft in the sequel to the Sherlock Holmes film Guy Ritchie directed with Robert Downey Jr and that sort of part is fun," Fry told the radio host, though he hinted that he longed for a role of more complexity, adding: "Just once in a while to play a genuine all-round sort of lead figure with complexity and tragedy and wit and all the sort of things that Oscar [Wilde] had [would be] a once-in-a-lifetime thrill."

In Sir Arthur Conan Doyle's original stories, Mycroft is the intellectually superior yet lazier Holmes sibling, who has a shady role in the British government. Also confirmed for the as-yet-untitled sequel are Swedish actor Noomi Rapace, who looks set to play the female lead, and Geraldine James, who will reprise her role as Holmes's landlady. Rapace won critical plaudits for her performance in the Swedish-made thriller The Girl With the Dragon Tattoo, based on the bestselling novel by Stieg Larsson.

The second Holmes film is rumoured to introduce the detective's regular nemesis, Moriarty, with actors such as Russell Crowe, Brad Pitt and Daniel Day-Lewis reportedly interested in the role. Ritchie's first film was a box office hit and fared decently with the critics – though the Guardian's Peter Bradshaw demurred, handing it just two stars out of a possible five. "It's a souped-up Victorian crime romp with Holmes and Watson reinvented as wisecracking action heroes," he wrote, describing Downey Jr and Law as "a two-man league of pretty ordinary gentlemen".