Sienna Miller goes braless under a blazer and baggy jeans as she joins dapper co-star Kevin Costner at the Horizon: An American Saga photocall during Cannes Film Festival

Kevin Costner and Sienna Miller were in good spirits as they attended the Horizon: An American Saga photocall during Cannes Film Festival on Sunday. 

The actress looked incredible as she went braless under a boucle beige blazer which she teamed with black wide legged jeans. 

Leaving her long blonde tresses loose in waves, Sienna, who plays Frances Kittredge, elevated her frame in a pair of eye catching gold metallic heels.

Meanwhile Kevin, 69, cut a dapper figure in a white suit which he teamed a matching open collar shirt and beige slip on shoes. 

The Hollywood actor, who plays pioneer Hayes Ellison who treks West through dangerous territory in hopes of a new life in the new film, wore a pair of black sunglasses.

Kevin Costner and Sienna Miller were in good spirits as they attended the Horizon: An American Saga photocall during Cannes Film Festival on Sunday

The actress looked incredible as she went braless under a boucle beige blazer which she teamed with black wide legged jeans

He was joined by his son Cayden who looked stylish in a white linen jacket and trousers which he donned with a blue T-shirt and trainers. 

It comes after Kevin debuted a haunting new poster for his $100m gamble movie series Horizon: An American Saga,

Horizon: An American Saga chronicles a multi-faceted, 15-year span of pre-and post-Civil War expansion and settlement of the American west.

The movie series is set to be released in two chapters on June 28 and August 16.

The first movie chronicles a 15-year span of pre-and post-Civil War expansion and settlement of the American west.

In the poster Kevin sports a moustache and hat, paired with a waistcoat and scarf as he stares into the sunset.

Kevin, who has been desperately trying to bring the four-part movie series to life for more than 30 years now, is thought to have personally raised up to $50 million of Horizon's $100 million budget with the move.

Leaving her long blonde tresses loose in waves, Sienna, who plays Frances Kittredge, elevated her frame in a pair of eye catching gold metallic heels

Sienna looked sensational as she arrived at the event wearing a pair of sunglasses

She accessorised the cool outfit with a pair of large gold hoop earrings

Meanwhile Kevin, 69, cut a dapper figure in a white suit which he teamed a matching open collar shirt and beige slip on shoes

The Hollywood actor, who plays pioneer Hayes Ellison who treks West through dangerous territory in hopes of a new life in the new film, was joined by his son Cayes

The pair are also joined in the film by (L_R) Isabelle Fuhrman, Ella Hunt and Abbey Lee

Horizon: An American Saga chronicles a multi-faceted, 15-year span of pre-and post-Civil War expansion and settlement of the American west

The movie series is set to be released in two chapters on June 28 and August 16

Kevin is said to have a net worth of around $250 million and was collecting a reported $1.5 million per episode of his hit show Yellowstone, making him the best-paid actor on TV.

Horizon also stars Sienna, Sam Worthington, Jena Malone, Michael Rooker, Danny Huston, Luke Wilson, Isabelle Fuhrman, Jeff Fahey, Will Patton, Tantanka Means, Owen Crow Shoe, Ella Hunt and Jamie Campbell Bower.

When Kevin introduced the trailer during a Zoom call with reporters earlier this year he shared: 'There was a great injustice incurred in the West, but it doesn't minimize the courage it took for my ancestors to actually cut loose and go there.

'And I recognize the resourcefulness it took, the bravery it took, to leave and make this march across this country.'