He was born in Ontario, Canada, to Pattie Malette, who was 18 at the time and in a casual relationship with his father Jeremy.
Jeremy left when Justin was three leaving Pattie as a struggling single mum.
Justin’s musical flair was obvious from an early age. In the film he is seen, aged five, in a home video peering out from behind a fringe and shouting: “Mummy, this is how I drum” – before banging out a rhythm on a plastic chair.
He taught himself to play four instruments and when he was only 12 he started busking outside a local theatre.
He made £2,000 one summer, playing covers of songs by his R and B heroes Usher and Neyo then took Pattie to Walt Disney World with the proceeds.
She posted a clip of him in a local talent competition – in which he came second – on YouTube and it became a sensation.
In 2008, hip-hop talent manager Scooter Braun clicked on one of Justin’s uploads by mistake and decided he should meet the young musician.
Justin and Pattie flew to Atlanta and Braun became his manager.
As Bieber fever spread, Usher began to battle it out with Justin Timberlake, who also wanted to mentor the young star.
Justin eventually signed to Island Def Jam Records, the label his hero Usher had joined aged just 14. First album My World went platinum in the US in 2009 with its follow-up My World 2 reaching No 1 around the globe.
He is now the biggest teen star since Michael Jackson.