'Young Sherlock' Reveals Its Moriarty & Mycroft

Guy Ritchie's Young Sherlock remains a family affair as the series finishes rounding out the main roster. As we've reported previously, Ralph Fiennes' nephew, Hero Fiennes Tiffin, will play the teenage version of Sherlock Holmes, and his other uncle, Joseph Fiennes, will also co-star in the production as Sherlock's father, Silas Holmes. The series also included the PBS family with Natascha McElhone (Hotel Portofino) playing Sherlock's mother, Cordelia. Now, two more actors have been confirmed as added to the cast, filling out the leading ensemble, one from the Amazon Studios family and the other the son of one of the U.K.'s greatest actors.

Max Irons (The White Queen), son of Jeremy Irons (Brideshead Revisited), is joining the Holmes family as Sherlock's older brother, Mycroft. The elder Holmes brother, who works for the British government in Doyle's original books, is more socially adept than his brother, though when the two get together, it's always obvious they are two peas in a pod. In the Young Sherlock books, Mycroft is in his mid-20s but still looking out for his younger sibling, who seems drawn to trouble.

The series has also cast Donal Finn, effectively pulling from the Amazon Studios family. Finn is best known as the actor who replaced the original Mat Cauthorn in Season 2 of The Wheel of Time. Finn joins the production as Sherlock's main nemesis, James Moriarty. The good news for Moriarty fans, who have watched the likes of Andrew Scott, Jared Harris, and even Ralph Fiennes himself excel in the role only to see his performance cut short with a long trip over the Reichenbach Falls, this Moriarty is still decades away from his fate.

Here's the series synopsis:

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 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.

Irons and Finn aren't the only ones confirmed since filming began. The series will also feature Zine Tseng (The Three-Body Problem) as Princess Gulun Shou’an and Colin Firth (Pride & Prejudice) as Sir Bucephalus Hodge.

Lead writer and showrunner Matthew Parkhill will pen Young Sherlock's episodes, with Guy Ritchie directing. Parkhill and Ritche will executive produce alongside Simon Kelton, Ivan Atkinson, Simon Maxwell, Dhana Gilbert, Colin Wilson, and Marc Resteghini, with Harriet Creelman co-executive producing.

Young Sherlock is expected to debut on Amazon's Prime Video sometime in 2025.