The 22-year-old singer and his former partner - who dated for a brief period in 2010 - were spotted talking with each other backstage at the MTV Video Music Awards on Sunday (28.08.11) and he admits it was great to see her again.
He told Kiss 108 radio: "She's really sweet. I got to see her and we got to catch up a little bit on the red carpet.
"We're going to try and find another time and not in all the craziness of the red carpet to be able to catch up. I'm happy that she's doing well and it was good to see her again."
Since his brief relationship with Demi - who entered rehab last November for three months to receive treatment for an eating disorder and self-harming - Joe has been linked to a number of high-profile stars, including 'Twilight' star Ashley Greene and Rihanna.
However, he has not been particularly strong on the subject of love, and has previously admitted he has had his heart broken by a woman.
He said: "I've been heartbroken. People like to think it's only girls that wind up heartbroken, but I've also had it happen to me."