Guillermo del Toro served as a back-up director on William Friedkin’s final film, The Caine Mutiny Court-Martial.

Producer Annabelle Dunne revealed during the movie’s press conference at the Venice Film Festival over the weekend that the late director, 87, was contractually required to have a back-up due to his age.

“That’s very common, Hollywood is ageist,” the producer admitted, describing del Toro’s involvement as a “state secret”.

According to Variety, Dunne then recalled raising the issue with The Exorcist director and he called her the following day suggesting the Pan’s Labyrinth filmmaker, who was a close friend.

“OK, honey I have the guy. Get a pen: it’s Guillermo del Toro, you got that?” Friedkin told her.

When the producer called up The Shape of Water director, he told her, “I am going to come to set every single day and sit next to you.”

Dunne added, “It was joy for all of us, including the actors, to have his presence there. He made it abundantly clear it was Billy’s movie. He said he was our mascot.”

Filming on the legal drama was completed before Friedkin died from heart failure and pneumonia on 7 August aged 87.

The Caine Mutiny Court-Martial, which stars Kiefer Sutherland and Jason Clarke, will be released via Paramount+ in the coming months.

© Cover Media