Sir Ian McKellen is due to star as an elderly Sherlock Holmes in the movie adaptation of 'A Slight Trick of the Mind', a 2005 novel by Mitch Cullin.

'The Hobbit' star has been signed on to portray the world famous sleuth which is set to be directed by Bill Condon, who he previously worked on in Oscar winning 1998 biography drama 'Gods and Monsters', with a screenplay by Jeffrey Hatcher.

The Holmes film is about the detective as an old man, partially crippled and only able to walk with a cane, and with an increasingly poor memory. He must crack a case that has stumped him for 50 years before his almighty mind finally fails him.

McKellen, who is 74-years-old himself, has a whole host of further movies due out over the coming months, including the two 'Hobbit' sequels 'The Desolation of Smaug' and 'There and Back Again', and Bryan Singer's 'X-Men: Days of Future Past'.

He will also appear in upcoming 18th century-esque comedy 'The Curse of The Buxom Strumpet', directed and written by Matthew Butler and also starring Gillian Anderson, Imelda Staunton and Mark Williams. Bill Condon's latest movie was 'The Fifth Estate' starring Benedict Cumberbatch - an actor who has also portrayed Sherlock in the BBC TV series.

Ian McKellen at the BAFTAs
Ian McKellen teams up with Oscar winning director Bill Condon in Sherlock flick