Saroo was only five years old when he got lost. He was travelling with his older brother, working as a sweeper on India's trains. "It was late at night. We got off the train, and I was so tired that I just took a seat at a train station, and I ended up falling asleep."
That fateful nap would determine the rest of his life. "I thought my brother would come back and wake me up but when I awoke he was nowhere to be seen. I saw a train in front of me and thought he must be on that train. So I decided to get on it and hoped that I would meet my brother."
Saroo did not meet his brother on the train. Instead, he fell asleep and had a shock when he woke up 14 hours later. Though he did not realise it at first, he had arrived in Calcutta, India's third biggest city and notorious for its slums.
"I was absolutely scared. I didn't know where I was. I just started to look for people and ask them questions."
Soon he was sleeping rough. "It was a very scary place to be. I don't think any mother or father would like to have their five year old wandering alone in the slums and trains stations of Calcutta."
The little boy learned to fend for himself. He became a beggar, one of the many children begging on the streets of the city. "I had to be quite careful. You could not trust anyone." Once he was approached by a man who promised him food and shelter and a way back home. But Saroo was suspicious. "Ultimately I think he was going to do something not nice to me, so I ran away."
But in the end, he did get off the streets. He was taken in by an orphanage, which put him up for adoption. He was adopted by the Brierleys, a couple from Tasmania. "I accepted that I was lost and that I could not find my way back home, so I thought it was great that I was going to Australia."
Saroo settled down well in his new home. But as he got older the desire to find his birth family became increasingly strong. The problem was that as an illiterate five-year-old he had not known the name of the town he had come from. All he had to go on were his vivid memories. So he began using Google Earth to search for where he might have been born.
"It was just like being Superman. You are able to go over and take a photo mentally and ask, 'Does this match?' And when you say, 'No', you keep on going and going and going."
Google Earth image that helped Saroo find his way home
He drew a circle on a map with its centre in Calcutta, with its radius about the distance he thought he had travelled. Incredibly, he soon discovered what he was looking for: Khandwa. "When I found it, I zoomed down and bang, it just came up. I navigated it all the way from the waterfall where I used to play."
Soon he made his way to Khandwa, the town he had discovered online. He found his way around the town with his childhood memories. Eventually he found his own home in the neighbourhood of Ganesh Talai. But it was not what he had hoped for. "When I got to the door I saw a lock on it. It look old and battered, as if no-one had lived there for quite a long time."
Saroo had a photograph of himself as a child and he still remembered the names of his family. A neighbour said that his family had moved.
"Another person came and then a third person turned up, and that is when I struck gold. He said, 'Just wait here for a second and I shall be back.' And when he did come back after a couple of minutes he said, 'Now I will be taking you to your mother.'"
Lost and found
• 1986: He loses his family and ends up living on the streets of Calcutta
• 1987: He is adopted by an Australian couple and grows up in Tasmania
• 2011: He finds his home town on Google Earth
• 2012: He is reunited with his mother in Khandwa
"I just felt numb and thought, 'Am I hearing what I think I am hearing?'"
Saroo was taken to meet his mother who was nearby. At first he did not recognise her.
"The last time I saw her she was 34 years old and a pretty lady, I had forgotten that age would get the better of her. But the facial structure was still there and I recognised her and I said, 'Yes, you are my mother.'
"She grabbed my hand and took me to her house. She could not say anything to me. I think she was as numb as I was. She had a bit of trouble grasping that her son, after 25 years, had just reappeared like a ghost."
"Although she had long feared he was dead, a fortune teller had told Saroo's mother that one day she would see her son again. "I think the fortune teller gave her a bit of energy to live on and to wait for that day to come."
And what of the brother with whom Saroo had originally gone travelling? Unfortunately, the news was not good. "A month after I had disappeared my brother was found in two pieces on a railway track." His mother had never known whether foul play was involved or whether the boy had simply slipped and fallen under a train.
"We were extremely close and when I walked out of India the tearing thing for me was knowing that my older brother had passed away."
For years Saroo Brierley went to sleep wishing he could see his mother again and his birth family. Now that he has, he feels incredibly grateful. He has kept in touch with his newly found family.
"It has taken the weight off my shoulders. I sleep a lot better now."
And there is something to make him sleep better - with memories of Slumdog Millionaire still fresh, publishers and film producers are getting interested in his incredible story.
Saroo Brierley spoke to Outlook on the BBC World Service
What a heartwarming story and I want to keep it hence the post