Vin Diesel has again been talking about the difficulty of making Fast & Furious 7 without Paul Walker.

His co-star was killed in a tragic road accident last year - and the movie's production was put on hiatus for several months.

When it resumed, Paul's brothers Caleb and Cody were recruited to fill in for the actor in certain scenes.

The Sun quoted Diesel as saying: "There's only one Paul Walker. When you've worked with someone for 15 years and you know each other's idiosyncrasies and you've created magic together for so long, it's a strange thing to mourn that person and simultaneously pretend that person is next to you.

"It was validating in a way that his family cared so much about the saga and the continuation and the completion of Paul's last work, but it didn't make the process any easier."

The movie is set for release next April - and it has been reported that one of the Walker brothers will become a franchise regular.