Demi Lovato says Justin Bieber has ''changed for the best''.

The former Disney star is proud of how Justin, 21, who has previously been in trouble with the police and been blasted for his attitude, has grown up over the past year as she knows how hard it is being a young performer in the public eye.

Demi, 23, who is close friends with Justin's ex Selena Gomez, 23, explained: ''I think everyone's got the fever again. Good for him. He's really changed for the best. The hardest thing is growing up in this industry. I went through it and the thing is, when you hit a certain amount of success you also still have to figure out how to be a teenager. It's the most confusing time in anyone's life.''

Demi also praised her pal Iggy Azalea and singer and actress Jennifer Lopez as women she looks up to.

Speaking to Rickie, Melvin and Charlie on KISS FM Breakfast, she said: I'm really close with Iggy. She's awesome. I love her and Jennifer Lopez. She's incredible. She's a woman that I look up to and not as Jennifer Lopez, but as a business woman. She's had to run her business. She's so talented and she's a boss. I told her just recently. I was like, 'You are boss with the biggest heart.'''