The singer-and-actress - whose brief romance with the Jonas Brothers star ended in May - insists their relationship has never got in the way of the original bond they had when they first met on the set of 'Camp Rock' in 2007.
She said: "Well. we started off as best friends and then we took it to the next level and it didn't work out. It wasn't meant to be but we're back to being best friends."
Demi - who turns 18 tomorrow (20.08.10) - also spoke about being bullied at school and admitted it saddens her when she hears of other young people going through similar experiences.
She said in an interview on US TV show 'Fox and Friends': "When I was younger, I went through bullying.
"It's a topic that's very sensitive to me that I can relate to a lot. And there are so many kids nowadays, I'm sure you've seen it all over the news; you hear about as young as 9-year-olds taking their own lives from what they deal with at school."
Earlier this year, Joe pledged to stay friends with Demi after they ended their relationship.
He said at the time: "Demi and I knew going into our romantic relationship that it may not be an easy one. I realise over the time we have shared together that I feel I care more about our friendship right now. It was my choice to break-up, but I love her as a friend. She's been there for me when I needed her. I will continue to be her friend and be there for her."