Julianne Moore is to play the world's worst witch in 'Seventh Son'.

The 'Single Man' actress - who recently signed up to portray failed US vice presidential candidate Sarah Palin in new TV movie 'Game Change' - will star alongside Jeff Bridges in the horror story, originally named 'The Spook's Apprentice'.

The movie follows the tale of a young boy, originally intended to be played by British star Alex Pettyfer before he dropped out, who is training to be an exorcist in the 1700s.

However, trouble begins brewing when he accidentally releases the most evil witch in the world.

Jennifer Lawrence was also offered a leading role but her recent decision to sign up to 'The Hunger Games' mean she can no longer partake, Bloody Disgusting reports.

'Yakuza Girl' filmmaker Sergei Bordrov is directing the project, which has been written by Max Borenstein.

Julianne, 50, has a number of big roles coming up following her turn in Oscar-nominated movie 'The Kids Are All Right' - as well as 'Crazy, Stupid, Love.' she has also signed up for 'Another Bulls**t night in Suck City'.