The new series continues at 8.30pm on Sunday night on BBC One with ‘The Sign Of Three’, written by Stephen Thompson, Mark Gatiss and Steven Moffat.

Cumberbatch commented: “There’s a lovely arc there which gives a lot more insight into them as brothers and where they came from. There is a really interesting glimpse of the hold they have over each other which hasn’t really come to light until this series. It’s great, Mycroft becomes the bigger brother in every sense – both intellectually and in terms of power. They are brothers in a family, they are blood relatives and that’s explored in more detail which is exciting – funny, but not trite. It’s quite profoundly moving I think.”

The Star Trek Into Darkness actor added: “You find out a bit more about both characters but the most interesting thing is that you find out a lot more about why he is the way he is, you have little hints of back story which just remind people that he grew up – he wasn’t just born Sherlock.”

He teased: “Sherlock was somebody who may have been a little bit different as a child but he is very much self-styled; he wasn’t born the way he is there’s a lot of conditioning that’s made him this genius, thrill seeking, adventurous, crime-solving hero that he is.”

> Find out all the details on Series 3 in our news summary.

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> Order Series 3 on DVD on Amazon.

> Buy the Series 1-2 boxset on Amazon.

Watch the Series 3 teaser trailer…