It’s the love story that took the internet by storm – but not for the reasons you’d expect.

Simply titled Evan, the 2:28 minute video follows a high school kid of the same name, who – in the run-up to the summer holidays – finds himself bored. So bored, in fact, that he feels compelled to write as much on the desk in his school library.

The next day, when he returns, he finds the words, “Hi bored, nice to meet you”, pencilled in underneath his own – and it sparks a flurry of  back-and-forth messages between Evan and his mysterious friend.

It’s clear that a romance is building, but, with the last day of school looming ever closer, Evan becomes increasingly worried that he won’t be able to track down his pen-pal. Will he be able to find her before it’s too late?

Watch the video for yourself below before reading ahead:

Throughout the video, it seems as if we are working through the motions of a typical high school romance – yet there’s no denying that Evan’s story is captivating.

And that’s the point; his story is too captivating. Which is why the ad’s shock ending feel as if it has come completely out of nowhere.

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“While you were watching Evan, another student was showing signs of planning a shooting,” the video warns us. “But no one noticed.”

It then runs us back through Evan’s story, turning the camera on a boy in the background; we see him reading a magazine about weaponry, watching violent videos on the internt, and even posting selfies of himself with a gun to social media.

We also see his troubled relationship with his fellow students and teachers; he argues with them in the corridors, he ignores them when they ask him for help, and he mimes shooting his teacher as he walks past during class.

All of this went completely unnoticed by everyone – including viewers at home. And it’s for this reason that we wind up at our tragic conclusion.

The video was created by BBDO New York in association with Sandy Hook Promise, a non-profit company led by the parents and families of the 20 children who were shot  and killed at Connecticut’s Sandy Hook Elementary School on 14 December 2012.

Recognised as the deadliest mass school shooting in US history, the Sandy Hook Massacre began some time before 9.30am that same day, when 20-year-old Adam Lanza shot his mother four times in the head with a .22-calibre rifle.

He then stole her car and drove to Sandy Hook Elementary School, where he broke into the school hall; Principal Dawn Hochsprung, school psychologist Mary Sherlack, and teacher Natalie Hammond went to investigate the strange sounds – and managed to raise the alarm before he turned his gun on them. Hochsprung and Sherlack were killed during the encounter, but Hammond, who was shot in the leg, was later taken to hospital and treated for her injuries.

Lanza made his way through the school, fatally shooting teacher’s aide Anne Marie Murphy, before forcing his way inside a first-grade classroom. Here, he found supply teacher Lauren Rousseau attempting to hide her young pupils – all of whom were aged between 6 and 7-years old – in the bathroom.

He shot and killed Rousseau, fifteen children, and behavioural therapist Rachel D’Avino.

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Lanza then broke into a second classroom and shot at the children hiding under their desks, killing them and their teacher, Victoria Leigh Soto, who attempted to dive in front of them and protect them from the bullets.

When police arrived at the scene, Lanza turned the gun on himself and committed suicide. To this day, investigators have been unable to establish why he targeted Sandy Hook Elementary School.

It is hoped that Evan, which has been released alongside the fourth anniversary of the Sandy Hook Massacre, will raise awareness about the dangers of school shootings – and encourage people to speak out when they recognise dangerous behaviour in others.

Greg Hahn, chief creative officer of BBDO, explained: “Through Evan we sought to show how different your perspective can be when you're aware of the signs. We've been fortunate to work with the inspiring people at Sandy Hook Promise to help parents, students and teachers better identify these signs.”

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Nicole Hockley, who founded Sandy Hook Promise after losing her young son Dylan in the massacre, said: “When you don't know what to look for, or can't recognize what you are seeing, it can be easy to miss warning signs or dismiss them as unimportant. That can lead to tragic consequences.”

According to Sandy Hook Promise, 80% of school shooters and 70% of individuals who complete suicides told someone about their plans before taking action.

But in the majority of cases, tragically, hardly anyone ever intervenes.

“It is important for us to show youth and adults that they are not helpless in protecting their community from gun violence—these acts are preventable when you know the signs,” explains Hockley.

“Everyone has the power to intervene and get help. These actions can save lives.”