ITV also confirmed that two new stars have joined the cast – Sir Lenny Henry and Roy Hudd.
It has not been announced what characters Sir Lenny, 57, and Roy, 80, will play but they will join regular cast members including Jodie Whittaker and Andrew Buchan who are returning as Beth and Mark Latimer.
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Olivia Colman and David Tennant have started filming the final series of Broadchurch
Arthur Darvill is also back on screen as local Vicar Paul Coates, Carolyn Pickles as newspaper editor Maggie Radcliffe, Charlotte Beaumont as Mark and Beth's daughter Chloe and Adam Wilson as Ellie's son Tom.
Other cast members include National Television Award winner Julie Hesmondhalgh, BAFTA winner Georgina Campbell and actors Sarah Parish, Charlie Higson and Mark Bazeley, who all play significant roles in the eight-part series.
The new season sees a brand new case for Detectives Miller and Hardy, who are investigating a serious sexual assault.
A year of research was carried out, focusing on Dorset-based organisations who specialise in dealing with victims of sexual assault, and police advisors who specialise in investigating crimes of sexual violence.
Sir Lenny Henry has joined the cast
Filming will continue in Dorset and Somerset throughout the summer, which have featured as locations in Broadchurch series one and two.
Producer Chris Chibnall said: "This is the final chapter of Broadchurch. We have one last story to tell, featuring both familiar faces and new characters. I hope it's a compelling and emotional farewell to a world and show that means so much to me."
Producer Jane Featherstone added: "We will return to the town and characters we know so well as they find themselves caught up in a new and compelling story which will test the strength of the community and the people who live there, and will, I hope, be a fitting end to this trilogy."