Vin Diesel continues to mourn the death of his friend and "Furious 7" costar Paul Walker. And the action star found an unlikely form of therapy in his latest role as an immortal witch hunter in "The Last Witch Hunter."

"Death was a huge theme last year," Diesel told The Associated Press Friday. "There was something therapeutic about playing this role after going through [Walker's death]. The idea that someone immortal could be so melancholy."

Walker died tragically aged 40 in a car accident on November 30, 2013 on hiatus from "Furious 7" production.

"2014 was a tough year for me in some ways — a lot of ways," Diesel said. "Playing a character that was masking his sorrow — his loss — was very appropriate for the time, because that's what I was doing in real life with the post-Furious 7."

Diesel said Walker would be proud that the "Furious" franchise will continue on without him. On Thursday it was announced that F. Gary Gray will helm "Furious 8." The news comes after Diesel revealed via Facebook that the next installment will be a trilogy.

"He took a lot of pride in this franchise and he'd be smiling down at the idea of us actually doing what we talked about, which is going to the 10th chapter," Diesel said.

"The Last Witch Hunter" hits theaters on Oct. 23. Watch the trailer below.

https://www.youtube.com/watch?v=xsuG2JUgs_8