"It was like a 20ft-high brick wall coming at us," recalls Rob Forkan of the monstrous wave which changed his life so drastically on Boxing Day 2004. Rob and his younger brother Paul scrambled onto the roof of their Sri Lankan guesthouse as the tsunami that would kill more than 230,000 people came into view.
As the killer wave hit, Rob managed to cling onto the roof with one hand and his brother's arm with the other.
Fighting against the power of the water, he knew if he let go, the chances were good that he would never see him again.
"When I was hanging on to Paul on that roof, pulling against the water… if you asked me to do that again now, I couldn't.
"But in that situation, I got some sort of weird inner strength. It was bizarre."
Ewan McGregor's latest box-office big hitter, The Impossible, is the heart-wrenching tale of one family who survived that terrible day.
But it's easy to see why friends of Rob and Paul claim the Londoners' story would make a better film. Tragically, their parents were two of the 149 Britons killed in the tsunami, while Rob and Paul, now 25 and 23, somehow made it back home.
But despite their loss, they are now trying to create a happy ending to their story – by using the memory of their mum and dad to help some of the world's poorest children.
It was 2000 when Kevin and Sandra Forkan decided to take Rob and Paul – then 15 and 13 – out of their school in Croydon to travel the world, along with their younger sister Rosie and younger brother Matty. "It was crazy," remembers Rob. "They packed up our house we'd been in for 20 years and got rid of everything. Each of us was allowed to take one bag – that was it."
The boys would spend most of the next four years moving around India with their family.
"It was a bit random," says Rob. "Our dad would read something in a book and then tell us we were going there the next day – pack your bags! That's how we ended up in Sri Lanka. Dad opened up the book and just decided he wanted to go there."
That was December 2004, just one week before Boxing Day; the day that would change their lives for ever. The family were staying in a guesthouse in Weligama, a coastal town in the south of Sri Lanka.
Aged 17 and 15, Paul and Rob were staying in a separate building to their parents and the two younger children, who were in a house about 30m closer to the shore.
"I remember Rob waking me, saying there was water in the room," says Paul. "We went outside and the water wasn't very high at that point, so there was no real panic – it just seemed weird. Then we started to hear the screams. That's when people saw it coming."
Stuck on that guest house roof as the wave threw all kinds of debris at them, they knew they had just one job once it passed: finding the rest of their family.
Incredibly, within a couple of hours they had found Matty, 13, in a tree and Rosie, just eight, being looked after by a group of surfers. Their parents, however, were nowhere to be found. Rob led the other three children through the devastation to a temple where they could take shelter and then went out to look for them.
He explains: "There was a young local lad who had lost his mum, so he said he would help me find mine. We were riding around for hours on bikes, checking everywhere. At one hospital, there was a football pitch full of bodies. I looked through them all."
When he got back to the temple, Rob got the news he had been dreading: some local waiters had found his dad's body, some 700m inland. But there was still no sign of their mother. Frantically, they continued to look for her. "I remember us both being convinced we had seen her on a bus that day," says Paul. "We went chasing after it, shouting and throwing rocks, trying to catch it. We were both sure we saw her, but it's weird what your mind can do."
As the eldest, Rob soon realised it was his responsibility to look after his siblings.
"I knew my parents would have wanted to get them all home, so I knew we just had to get Colombo, the capital. The weird thing was all the adults on holiday who were freaking out, screaming and crying. I was just thinking about pulling our shit together and getting out of there."
Stranded in a devastated country, with no money, ID or possessions, that was easier said than done. For days, they slept rough and scavenged food wherever they could to survive, all the while hitchhiking towards the city. It was more than 200km and yet Rob managed it, getting the four of them to the British embassy in the capital within a week.
Rob believes that without their previous travelling experience, they might not have made it. "The petrol pumps were down, the railways had been wiped out and we had nothing. That's pretty difficult, but we'd been given a load of survival skills, which are not things we would have learned going to school. To start with, there was just no food, so I was boiling water and putting sugar in it, just so we had something. Even our family don't really understand how we made it back.
"When we reached Colombo and I managed to call my older sister Marie in the UK, she was so freaked out that she didn't even know who it was on the phone. She had been watching the news for days, so she was convinced we were all dead."
Once back home, it was a punishing return to normality. Because Rob and Paul had never seen the bodies of their parents, the rest of the family refused to believe that Kevin and Sandra were gone.
In the end, it took three months for their parents to be formally identified, at which point Paul and the two youngest children were all adopted by Marie – and the struggle to continue with life could begin.
Then, a year ago, Rob and Paul had an idea: to create a company that sells flip-flops. But Gandy's (named after the time when Paul woke up at a festival "with a mouth like Gandhi's flip-flop") is a company with a big difference.
Inspired by what they learned from their parents, who donated large chunks of money from their fashion business to charity, Rob and Paul are not attempting to make money for themselves. The main goal of the business – which has the slogan, "orphans for orphans" – is to raise money for deprived children in Goa, India.
As well as providing food and medicine, Gandy's is already funding a teacher and school equipment for 100 children for a year.
"It's where we spent a lot of time as kids," explains Paul. "But most of all, it's where we have the best memories of our mum and dad. That's why we want to leave something there."
With multi-millionaire investors now part of their business, their aim is to raise enough money to build an orphanage in India before the 10th anniversary of the tsunami, as the ultimate tribute to their parents.
And Rob believes it is the same skills that saw him lead his siblings to safety that will see him succeed, even without any academic qualifications.
"People say how intimidating it must be to deal with big retailers, and we just say, 'No, trust us. We know what intimidating is. We know what a challenge is. It might sound crazy, but we don't have any real fear any more. We know that nothing is impossible.
We're trying to create something positive out of a negative. Our parents believed in the idea that if you fall off your bike, you get back on it. There's no point in feeling sorry for yourself and doing nothing with your life. We had an incredible experience with the travelling we did, and I wouldn't change that for the world, even with everything that happened."
So given the incredible nature of their story and their bright prospects for the future, does Rob think their tale could make a movie?
"Let's give it another five years and see where we are then. People loved The Social Network, which was about a guy creating an amazing business, and people like The Impossible, which is about the story of the tsunami. Maybe we can make a film that's a mix of the two…"
'The Impossible' is out now on Blu-ray and DVD