In "After Earth," a hero is born. A hero who scales impossibly steep cliffs. A hero who soars through the air with a wing-suit. A hero who wields a dual-bladed staff against a vicious alien enemy.

But that hero is not Will Smith. It's his son, Jaden Smith, who gets the bulk of the "After Earth" action. The real-life father-son duo play a fictional father-son duo trapped on a far-future Earth, a deadly planet that's become uninhabitable for mankind. With the father seriously injured, it's up to the son to set out into the unforgiving wilderness and find a way off the planet.

The premise tasks Will Smith with taking a literal backseat as his son steers the adventure forward. Not that the "Independence Day" and "Men in Black" superstar is complaining about passing the action-hero torch, mind you.

"As a parent, it was great to watch him grow and develop," the elder Smith told MTV News of Jaden's work on the M. Night Shyamalan-directed movie. "There were things that were pretty edgy, stunt-wise, with a certain amount of difficulty. When people see the sequences cut together, it's magical."

[article id="1708222"] How "After Earth" Reflects Will And Jaden Smith's Relationship.[/article]

Jaden's preparation for "After Earth" consisted of four months of training in areas ranging from rock-climbing to parkour. The 14-year-old actor also immersed himself in staff-training to learn how to use the Cutlass, a two-sided blade that soldiers in the "After Earth" universe wield during combat.

But for Jaden, the "After Earth" experience wasn't just a matter of learning new skills. It was a physical transformation, too. By the end of production, he had gained 20 pounds and grew four inches -- a very happy development for the young actor. "I was pretty stoked," he admitted.

Considerably less stoked was Jaden's father.

"I was proud of that growth as a parent," Will clarified. "But it sucks as a producer. It was like having two different kids in this movie!"

Difficulties as a producer aside, Will has nothing but pride in the work his son put into "After Earth." "He did a really fantastic job in this movie," he said. And for Jaden, the transformation was life-changing.

"I grew so much during this movie," he said. "It was a transitional phase for me."

Check out everything we've got on "After Earth."