Clive Myrie reports from Oregon on Willy's bid for freedom

He was captured at the age of two and has spent most of his life performing for audiences in the Reino Aventura amusement park near Mexico City.

Keiko performing in Mexico

But the pool there was small and the water too warm for him.

He developed skin lesions, flabby muscles, became prone to viruses and at 3490kg was a tonne underweight.

A foundation - partly funded by the makers of the film - paid for him to be shipped to an aquarium in Oregon in the US for rehabilitation two years ago.

Keiko was airlifted from Mexico to Oregon in the US

He has now recovered his health, gaining 860kg in 18 months, and is ready for the next stage - shipment to a sea pen in his native Icelandic waters.

"It's been a very speedy recovery," said Diane Hammond of the Free Willy Foundation.

"When we first saw him we thought it would take a great deal of work and time to get him anywhere close to what he is now."

Having spent so long in captivity, he has had to re-learn natural behaviour like catching fish for himself - something that has never been done before.