Saroo Brierley: The real-life search behind the film Lion

Sunny Pawar as five-year-old Saroo in the new film Lion

He was the tiny boy from a poor family in India who fell asleep on a train and woke up 1,000 miles from home.

After fending for himself on the streets, five-year-old Saroo made it to an orphanage, where he was adopted by Australian couple Sue and John Brierley to begin a new life in Tasmania.

Years later, as a young man, he yearned to discover more about his origins. So he began an ambitious Google Earth search that would prove to be fateful.

Now his story has been told in Lion, a Hollywood film starring Dev Patel and Nicole Kidman.

The search

The image of Saroo's birth mother burned in his mind. He set out to find her with a laptop and unwavering determination.

It became an obsession. For years he pored over satellite photos night after night.

"I used mathematics and everything I could remember about the landmarks and the architecture of my home town," Saroo tells the BBC.

Saroo Brierley first chronicled his story in his book, A Long Way Home

Then one day he found it. A dusty village in central India filled with childhood memories - the forest, the temple, a little bridge, a brick wall, the waterfall where he used to play.

Memories of his mother swirled. He wanted to tell her: "I know you looked for me, but I spent my whole life looking for you."

Next chapter

Saroo wrote down his experience - including what happened next - in a memoir that spawned Lion, which opens in the UK and Australia this week. It has already screened in the US, and is hoping to generate awards buzz.

"I never thought that something like this would come to someone like me. I'm a pretty laid-back kind of person," Saroo says.

"People are just so enthralled and enchanted by the movie."

When his book achieved success, Saroo took time out from his job selling industrial equipment in his father's business in Hobart. Now he has a packed schedule of film promotional tours. His life has changed again.

Saroo's adoptive mother, Sue, hopes the film could help transform other lives too.

"Sadly we've got a lot more war happening [now] and I believe there are just as many children wishing they could join a family," she says.

"They're orphans of war, and just abandoned in camps." Adoption should happen "a lot more", she says.

Lion is the fifth film British actor Dev Patel has shot in India

The film's cast has also supported fundraising to help the millions of children living on India's streets.

Nicole Kidman has said she was moved to tears by the film's "beautiful" depiction of an adoptive mother's love.

"I really admire her as an actress," says Sue. "She's Australian, she's an adoptive mother - we're really on the same page."

Slumdog Millionaire star Patel spent eight months honing his Australian accent, bulking up and growing his hair out for Lion.

"His devotion in this film has just been amazing," Saroo says.

As for himself, Saroo says he has returned to India more than a dozen times, but Tasmania remains home.

"That's where my heart is, that's where my family is, that's where my friends are," he says.