NEW YORK (AP) — Vin Diesel still struggles over the loss of his friend and "Furious" co-star Paul Walker, so taking on the role of an immortal in the upcoming film "The Last Witch Hunter" helped him deal with his grief.

"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)."

Diesel is no stranger to fantasy and sci-fi films, having starred in "The Chronicles of Riddick" series, "Babylon A.D.," and "Guardians of the Galaxy," but this one was special for him.

"The idea that someone immortal could be so melancholy. 2014 was a tough year for me in some ways — a lot of ways," Diesel said, choking up before continuing. "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."

Walker died in late 2013 after the Porsche in which he was a passenger crashed and burned north of Los Angeles during a holiday break in the filming of "Furious 7," the latest installment of "The Fast and Furious" franchise. Production was halted indefinitely, but resumed seven months later. Diesel felt continuing the film would honor Walker's legacy, and his respect for the series' devoted fanbase.

"Paul said, 'You know ("Furious) 7" could bomb and ("Furious) 8' is still guaranteed.' When somebody who is like your brother makes a promise, you feel inclined to want to honor that," Diesel said.

Diesel shared Walker's vision on the longevity of the series.

"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.

While that remains unclear, "Furious 8" is confirmed for a 2017 release, and rumors had circulated that Diesel would direct that installment. The actor has previously directed a short called "Los Bandoleros" with the "Furious" cast that explains each character's backstory.

But Diesel dismissed the notion of getting back behind the camera for a feature — at least for now — despite pressure from a source very close to the actor.

"My mom wants me to direct tomorrow," Diesel said, "I'm like, 'Mom, it takes about a year of your life to go and direct. There's so many other movies I got to make.'"