LONDON (Reuters) - The heartwarming true story of a stray cat that helped change the life of a London busker musician gets a big screen adaptation in "A Street Cat Named Bob" that premiered in the British capital on Thursday.

Based on the book of the same name, the film stars "Clash of the Titans" actor Luke Treadaway as James Bowen, a recovering drug addict who upon returning from busking one evening in 2007 found an injured ginger cat at his sheltered accommodation.

Bowen nursed the animal, which he named Bob, back to health and soon realized the cat was inseparable from him, following him as he went busking in London's central Covent Garden area.

The sight of Bob on Bowen’s shoulders or sitting by his feet as he performed on the streets caught the attention of increasing numbers of passersby and led to a life turnaround and bestselling book for the busker.

“He gave me a reason to get up in the morning ... and now I’m standing here," Bowen told Reuters on the red carpet with Bob perched on his shoulders. “A movie about a part of our lives is just mind blowing."

While producers had several cats on hand for the shoot, Bob also starred as himself, with co-stars Treadaway and "Downton Abbey" actress Joanne Froggatt describing him as "a professional" on set.

"It was kind of an unusual experience filming in Covent Garden with real Bob on your shoulders but it was amazing," Treadaway said. “He would just know what he had to do."

Bob lay on Bowen's shoulders throughout media interviews on the red carpet ahead of the film’s screening, for which the two were joined by Prince William's wife Kate, who attended as patron of the Action on Addiction charity.

Fans cheered as they saw Bowen and Bob, with some saying they had traveled from as far as the United States for the premiere.

(Reporting by Francis Maguire and Marie-Louise Gumuchian; editing by Mark Heinrich)