Exclusive: Guy Ritchie’s Young Sherlock series has cast the title character’s older brother. Max Irons (Condor) is set as a series regular on the Prime Video show, playing Mycroft Holmes opposite Hero Fiennes Tiffin’s Sherlock. Speculation about Irons’ casting started last month when he was snapped on the set of the series; his character had not been revealed until now.

Inspired by Andy Lane’s book series, Young Sherlock is described as an irreverent, action-packed origin story of Sir Arthur Conan Doyle’s beloved detective in a re-imagining of this iconic character. At age 19, Sherlock Holmes (Fiennes Tiffin) is disgraced, raw, unfiltered, and unformed, when he finds himself caught up in a murder mystery at Oxford University which threatens his freedom. Diving into his first-ever case with a wild lack of discipline, Sherlock manages to unravel a globe-trotting conspiracy that will change his life forever.

In addition to Fiennes Tiffin,...