And, it sounds like their meeting has been a long time coming!
Sharing a photo of the pair together, Olly said: "Yesssss @ddlovato Great to hang out finally. What a singer!!"
Well, it's no wonder Olly looked so excited then, as he's clearly been waiting a while for his chance to cuddle up to Demi.
The pair have recently collaborated on 'Up' a track from Olly's brand new album, Never Been Better and judging by Olly's tweets, Demi joined him to perform their single during an acoustic performance earlier today.
Ahead of Demi's arrival, Olly tweeted: "Acoustic performance is in progress... Just waiting on a special guest."
Wow - those lucky fans watching were in for a treat!
The pair's performance comes after Demi was spotted jetting into London yesterday.
Heading to the UK to support Enrique Iglesias on his upcoming 'Sex and Love' tour, it seems the pop princess made sure to squeeze in a quick visit with the former Xtra Factor co-host before hitting the road.
Meanwhile, Olly has recently announced he has landed his own TV show, A Night With Olly Murs.
Set to air on ITV later this year, Olly's TV special promises comedy, celebrity guests and of, course, musical performances from the man himself.
Sounds good to us!
Reveal is now on Google Plus! Join us here for the latest pictures, fashion and celebrity news!