The Sully star reveals he strapped on the gloves and stepped into the ring for fitness when he had to get in shape for 2000 movie Erin Brockovich, and it has become a big part of his life ever since.

"I learned a skill to get in shape for this Hollywood career," he tells WENN. "I always say to young actors, 'You got to learn how to ride a horse, shoot a gun and throw a punch, because if you learn those things early you're going to do that in your career and you want it to look second nature.' So I chose boxing.

"I work it into my work-outs every single day, so if I'm doing sit-ups I always come up into a punch. Whatever I do I always incorporate boxing into it, which really helped me out in this movie."

Unfortunately, Aaron couldn't work with the real Rooney because "he got hit in the head a lot (so) he's in the hospital with dementia", but he studied with the trainer's son - and some of the biggest names in boxing.

"I went through training camp with Manny Pacquiao. Freddie Roach (Manny's boxing coach) let me be a fly on the wall... and I was in the training room before and after the fight.

"I was ringside with (sports writer) Larry Merchant. I got a very good education about boxing and its mentality and the sacred trust between the two fighters and their brotherhood. That was invaluable for me."