Just days after the former Australian swimming champion's unexpected comeback, Grant Hackett's father has revealed that the sleeping pill addiction which ruined his son's personal life and tarnished his career, was triggered by a death threat. Former police inspector Neville Hackett said that his son had 'his life threatened by a well-known associate of criminals' two years ago, leading the swimmer to immediately hop on a plane to his parent's home in the Gold Coast. 'I know he used Stilnox while he was swimming but he wasn't hooked on it. It was when his life was threatened and he couldn't sleep at night from all the worry,' Hackett senior told The Daily Telegraph. Scroll down for video . Grant Hackett's father has revealed the swimmer's sleeping pill addiction was triggered by a death threat . The revelation comes after the 34-year-old made a come back last Sunday when he earned a 2015 world titles relay team berth by cruising to fourth place in one minute and 46.84 seconds . 'That's what really caused the Stilnox abuse and the addiction.' Hackett senior admitted that while the threat was never reported to police, it was taken very seriously by the swimmer's family. The dual Olympic champion appears to have recovered from his tumultuous year, which ended with  a five-week stint in an Arizona rehab clinic. Following his swimming comeback on Sunday night, in which he earned a 2015 world titles relay team berth by cruising to fourth place in one minute and 46.84 seconds, Hackett reflected on how much he had turned his life around in the past 12 months. Former police inspector Neville Hackett (centre) said that his son had 'his life threatened by a well-known associate of criminals' two years ago . The addiction to Stilnox which ensued, led Hackett's personal life to fall apart last year. It also began around the time he divorced Australian singer Candice Alley in August 2013 . 'If you had asked me 10 years ago if the only thing that got me on the team was on the relay it would be bitter disappointment,' Hackett said. 'But right now, it is one of the biggest achievements of my life.' The 34-year-old made the team after only six months of training following a six-year layoff, with his training schedule involving 55-60km of swimming a week and three gym sessions, according to coach Denis Cotterell. While Hackett's personal life fell apart last year due to his sleeping pill addiction, his professional demons went back as far as his last major meet, the Beijing 2008 Olympic Games, where he was denied a record third straight 1500m gold medal. The dual Olympic champion said, following his Sunday night achievement: 'If you had asked me 10 years ago if the only thing that got me on the team was on the relay it would be bitter disappointment, but right now, it is one of the biggest achievements of my life' He made the team after only six months of training following a six-year layoff, with his training schedule now involving 55-60km of swimming a week and three gym sessions, according to coach Denis Cotterell (pictured) 'I will be honest. I hated the sport for a long time,' Hackett said. 'I got scared getting into a bathtub. 'To discover a love for something that has been such a big part of my life is really pleasing now because I don't walk away with that taste of Olympic silver in my mouth by a few hundredths of a second. 'I can really enjoy the sport for what it is now.' Hackett had been adamant he had not even launched a comeback after entering the 2015 national titles. 'It was a challenging few years and I had to live it pretty publicly,' Hackett said . But, he allowed himself a moment to reflect on how far he had come in the past year while savouring the remarkable 200m result in which he shaved three seconds off his best time since his return. 'It was a challenging few years and I had to live it pretty publicly,' Hackett said. 'One thing I am good at is listening to people around me. 'I never sit there and feel too sorry for myself for too long. I take accountability for my actions - right or wrong. 'I tried to make the best steps forward - that is all I have ever tried to do.'
Hackett's father said son's life was threatened by 'associate of criminals'
The threats, made two years ago, were not reported to police .
Instead, Neville Hackett said his son turned to Stilnox sleeping pills .
It comes almost a week after Hackett made his comeback by earning a spot in the 2015 world titles relay team .