Sigourney Weaver is in negotiations to join the cast of The Mortal Instruments: City of Ashes, Constantin's sequel to its upcoming supernatural fantasy, The Mortal Instruments: City of Bones.

Much of the cast of the first installment, which opens Aug. 21 and includes Lily Collins, Jamie Campbell Bower, Kevin Zegers, Robert Sheehan, Jemima West and Jonathan Rhys Meyers, is returning -- as is director Harald Zwart.

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The project continues the story of a girl (Collins) who discovers she is a demon-slaying Shadowhunter and enters a world filled with warring vampires, werewolves and faeries, while also falling for another Shadowhunter (Bower).

In one of the few new roles, the veteran actress will play the ruthless leader of the Shadowhunters who will stop at nothing to destroy the man who killed her son.

An October start date is being eyed. 

A legend in the genre world for her Aliens work, Weaver’s recent appearances include Amy Heckerling's romantic vampire comedy Vamps, Cold Light of Day with Henry Cavill and cult hit Cabin in the Woods.

She is repped by UTA and Jackoway Tyerman.