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."

How "After Earth" Reflects Will And Jaden Smith's Relationship.

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."