The 26-year-old pop star dated the 'Cool for the Summer' singer in 2010, and following her battles with addictions and an eating disorder, Joe thinks Demi is currently in a very healthy frame of mind.
Asked about his one-time lover and fellow former Disney star, Joe said: ''She's the best version of herself I've ever known. She's healthy and that's obviously something a lot of the world knows now, but she's gotten over [the really hard part].
''I know a lot of friends who've gone through similar things and it's when you have to live with your new self for a few years - that comes with a lot of struggle. And being a pop star on top of that, that's a lot of pressure, but she's amazing at speaking truth to what she believes.''
Joe admitted he is envious of Demi's candid nature and her ability to be so accepting of herself.
He told Billboard: ''I wish I could have a bit more of that. Excuse my language, but she doesn't give a f**k. She goes out there and says, 'This is who I am.' Considering what we've all come from, it's not always easy. We feel like we have to be cautious.''
Joe's younger brother Nick, 23, is touring with Demi and he says it's ''cool'' to see how the two of them have grown up together.
Asked if he's surprised they have remained so tight, Joe shared: ''It's surprising just in the world we live in -- it's tough to stay friends with people who are in the industry over this much time. But they are two of the closest. They've seen each other go through so much, personally and in their careers.
''It's cool to see this bond now that they're adults. I think it's nice for an audience as well - they get to watch Nick and Demi grow up, not only together, but also musically.''
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