"I come from a wrestling universe where you try to make something look punishing, but the goal is for you and your partner to do it 300 nights a year and I thought is that how this movie is going to be? And it's not! Vin is all in."
Cena plays the long-lost brother of Diesel's on-screen character in the new movie.
And the Hollywood star admitted he can relate to certain elements of his character's story.
He told RTE: "We're human beings and I'm 44 years old and I have the regular scope of emotions that humans have, and it includes sadness, bitterness, anger, regret ... And a lot of times, unfortunately, those are portrayed against the people we hold closest to us.
"Families are tied closest together and I have certainly had my ups and downs with my siblings and my parents but that is a road we all go down in life."
Meanwhile, Diesel recently revealed he gave Dwayne "The Rock" Johnson "tough love" when he joined the Fast and Furious franchise.
The action star was rumoured to be feuding with his co-star in 2016, and he explained that, as a producer on the action series, he had a particular vision for the former wrestler's character, Luke Hobbs.
He said: "My approach at the time was a lot of tough love to assist in getting that performance where it needed to be."
