Justin Bieber found reading his mother's memoir ''tough''.

Pattie Mallette, 37, was sexually abused, took drugs and attempted suicide before becoming pregnant with Justin and splitting from his father Jeremy Bieber at the age of 18 and while her autobiography 'Nowhere But Up' was difficult reading for her son, Justin, 18, is supportive of her decision to write it.

He told Macleans.ca: ''Yeah, it was a lot for me to hear. But I'm older now. When I was younger, my mum never told me any of this stuff. It was definitely hard reading those stories, but I'm supportive of her writing the book. It's cool.''

Pattie's mother Diane and step-father Bruce Dale admitted they were shocked by some of the incidents in the book as they were unaware of many of her difficulties.

Bruce said: ''There are three sides to every story. There's one side, the other side, and then there's the truth.''

Meanwhile, 'As Long As You Love Me' singer Justin is determined to be more than just a ''teen heartthrob'' and says his competitive nature will help to keep him at the top.

He explained: ''I don't just want to be a teen heartthrob. Now I'm at the top, there's only one way to go and it's down. That gives me the motivation to stay on top and keep pushing. I grew up with a really competitive side, playing sports--basketball, hockey and soccer. I don't want to be second-best, third-best, fourth-best. I want to be the best. That takes a lot of dedication and hard work. You gotta have plans.''