SPOILER WARNING FOR THE EVENTS OF ‘THE LYING DETECTIVE.’ 

Most of us have had the best part of a week now to come to terms with the shocking revelation of ‘The Lying Detective’ – that Sherlock and Mycroft have a secret evil sister! Actress Sian Brooke, however, has been sitting on that particular juicy secret for a while – and it can’t have been easy.

Speaking at the BFI screening of Series Four’s finale episode ‘The Final Problem’, Brooke talked about the process of getting the role.

“I just thought it’s a little part in Sherlock, it’s lovely.”

However, then she was asked to audition for the other ‘bit part’ roles that Euros Holmes assumes.

“I just thought they couldn’t make their minds up! When they actually revealed what it was, I was like, what? What? WHAT?”

So how well did Sian keep the role a secret?

“They said you can’t tell anybody, which means you can’t tell anybody. Well, I had to tell my husband…”

At this moment, co-creators Moffat and Gatiss shouted “We said nobody!” to the delight of the crowd.

“I had to tell my husband and my mum and dad because they had to look after my kids when I was going to Cardiff. Everyone else was like ‘where are you disappearing to? What are you filming?’  and I said ‘I’m just filming a new crime drama’ ‘Who’s it for?’ ‘BBC’ ‘Who’s in it?’ ‘Everybody’s new, you won’t know anyone, they’re all new faces…’ I am so fed up of telling lies. I’m so relieved that it’s out.”

So how did Sian feel about fooling the entire Sherlock viewership like that?

“That was great because the main objective, reading it, was to be able to hide in plain sight so I think there’s a lot of people to thank in the make-up department and costume department and the way it’s so cleverly edited.”

Den of Geek