Jeff Horn initially got into boxing after finding himself the victim of bullies as a youngster.

In the wake of his greatest triumph, he found himself bullied anew – this time by online critics who refuse to accept his upset win over Manny Pacquiao.

Horn shocked the boxing world on Sunday, when he came away with a unanimous decision win over the "Pacman" to become the new WBO welterweight champion. It was an upset of massive proportions, as very few had given Horn a chance to be competitive against the Filipino star, much less to beat him.

Worldwide, athletes reacted with disappointment, and some, outright disgust. There were accusations that the bout was rigged, and stars from the NBA and the NFL made it known that they felt Pacquiao had been robbed of his rightful victory.

Teddy Atlas, the commentator, told Horn to his face: "I thought you lost."

Remarkably, their comments paled to those that are being posted on Horn's social media accounts, with boxing fans – and Pacquiao fans – not bothering to mince their words.

"You're an idiot boxer," wrote one fan. "You're a disgrace to the boxing industry," according to another. Another wrote: "You must feel like a fraud, being gifted that belt by the judges."

Several accused Horn of using "illegal tactics," a reference to the accidental head butts that opened up two gashes on Pacquiao's head midway through the fight.

According to a Daily Mail report, Horn's wife, Joanna, was also targeted by "trolls." His Instagram page is full of comments attacking his pregnant wife, most of them of the sexist, body-shaming variety.

Horn has not responded to the social media criticisms, instead opting to put victims of bullying on the spotlight after his great triumph over Pacquiao.

"I'd just like to say one thing. To all the kids out there in schools – I'm not saying Manny Pacquiao is a bully or anything – but I'm just saying, that this is a win for all you guys out there being bullied," Horn was quoted as saying.

As a child, Horn was a victim of bullying, with one episode in particular still clear in his mind after so many years.

He remembers how he and a friend were bullied by some 30 other children. One bully ordered his friend to get on his knees and apologize, and was still smacked in the head for his trouble. When told to do the same, Horn refused, and got slapped.

It was the episode that "sent me over the edge," Horn later told The Sydney Morning Herald. He felt "annoyed and so belittled" by the incident, even though it was not the first time that he had been victimized. He vowed to do something about the situation, and soon found himself training under the watchful eye of Glenn Rushton.

Rushton was at Horn's corner when the 29-year-old Australian pulled off the huge upset over Pacquiao, and was one of the few who were not surprised at the result.

Even as the backlash continues to flood in – both online and off – Horn chooses to remain unruffled. He has been the victim of bullying once before, and he has no plans of letting them taint his moment of triumph.

• FULL STORY: Horn brushes aside backlash over Pacquiao decision

"There is always going to be backlash, where people are going to say I was lucky or whatever," he said. "There are always naysayers saying I didn't win the fight."

"I think I won the fight, a lot of Queenslanders think I won the fight, and people around the world," he said. "So you will always have the select few that are against you."

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