Rebel Wilson was "so painfully shy" when she was growing up.

The 43-year-old actress always "struggled to express" herself during her childhood and decided when she was in her mid-teens to change things because she couldn't go on feeling like she was "in prison" with her lack of self-confidence.

Speaking on UK TV show 'This Morning', she explained: "I was so painfully shy, I was born that way. And it was something I wanted to change about myself but I didn't know how.

"One day I was eating my lunch in the library just by myself and I read this article saying that your personality at 15 will basically be your personality for life.

"And I thought 'Oh, well I don't wanna be...'

"It's not that there's anything wrong with being shy, I just couldn't really express myself to people and it felt like being in a prison at times. And so I wanted to learn.

"So I thought 'Well okay, I've still got some time' and I bizarrely came across this gym bag full of cassette tapes that my father had that gave all sorts of tips about improving your life.

"I guess they were kind of motivational tapes. He just had them in the back of the car and I started listening to them."

The 'Senior Year' star - who was born as Melanie Elizabeth Bownds - ended up "forcing" herself to do things like speak to strangers and while it was at first "really awkward", she eventually overcame her shyness and became one of the most "popular" girls in her school.

She said: "I just really wanted to overcome my shyness so I forced myself to do things like speak to five different people, new people, every day. Of course, at first it was really awkward and my face would go red. I'd be on the bus and I'd say to another girl and say 'How's it going? Are you going to school? Me too!' Stupid stuff.

"But then eventually I felt like...other people might be feeling lonely or isolated as well and me having a chat with them might've been the highlight of my day. Long story short, I did change my personality and became popular at high school."