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Dad's Army star Toby Jones will star as Sherlock's nemesis in one of the brand new episodes for series four, which is currently being filmed in Cardiff.

Toby will star alongside Benedict Cumberbatch and Martin Freeman, in the second episode of the brand new three-part series, which started filming today at the Cardiff University Student's Union.

Meanwhile student fans of the series were going Sherlock-crazy as they were stuck revising instead of out meeting their TV heroes.

Episode two will be directed by Nick Hurran, who was Emmy nominated for Outstanding Directing for a Miniseries for 'His Last Vow' series three Sherlock episode.

Toby Jones said: “I'm excited and intrigued by the character I shall be playing in Sherlock."

Co-creator, writer and executive producer Steven Moffat said: "Delighted to have Toby Jones on board, bringing to life one of Doyle’s finest villains."

Co-creator, writer and executive producer Mark Gatiss added: "We're thrilled to welcome one of our finest actors to the Sherlock family. I know Toby will embrace the part with true relish!"

We are on pins to find out who Toby is playing.