Demi Lovato's boyfriend has a ''weird'' friendship with her ex Joe Jonas.

The 'Neon Lights' hitmaker has revealed Wilmer Valderrama thinks her ex-boyfriend is a ''cool guy'' and also insists he isn't jealous of her working relationship with Joe's brother Nick.

She said: ''Nick and Wilmer get along great - Joe and Wilmer, too. It's weird.

''In the beginning, I was like, 'Why the f**k are you friends with Joe?' He was like, 'He's a cool guy.' Yeah, I know. I dated him.''

And the 22-year-old beauty has insisted her relationship with Wilmer has gone from strength to strength despite a few hiccups along the way.

She told Cosmopolitan magazine: ''We started dating when I turned 18 ... Right after that, I went to rehab. People told him, 'You should probably leave. She's on a spiral, and you're going to be sucked down with it.' But he was like, 'I'm not leaving. This is somebody I really care about.' We relate on a lot of levels. I've seen a lot of s**t, s**t people don't know about ...

''The only times we ever broke up were when I was relapsing, whether it was drugs or in a bad place and rebelling against everybody, not just him.''