Demi Lovato is "so happy" for her ex-boyfriend Joe Jonas and Sophie Turner following their engagement

Writing in the comments section of Joe's Instagram post, the 25-year-old brunette beauty wrote: "HUGE CONGRATS. Sooooo happy for the both of you! (sic)."

She then liked the picture, which shows Sophie's sparkly jewel sitting perfectly on her ring finger as she balanced her hand on Joe's, before following the 'X-Men: Apocalypse' star on her social networking sites.

Joe and Sophie - who have been dating since November - were first spotted getting close at a concert in the Netherlands earlier this year and have been inseparable ever since.

Sophie had previously admitted dating Joe can be "frustrating" because of the public scrutiny about their love life.

She explained: "You do feel like you're living in a fishbowl. It's frustrating [that] it's the most mundane things that make the news - how boring!"

And the 21-year-old actress has been trying to keep her relationship as private as possible.

She shared: "I'm in a relationship, but it's a very private relationship. I'm happier than I've been in a very long time. I very much isolated myself for a while and forgot what was fun. Going out with friends, going out to eat, not really having a care. And people I've met recently in my life have drawn me out of that. It really helps you own those insecurities. The things I tortured myself about before, I can forget about."

Since the news broke, Joe's brother Nick has also rushed to social media to congratulate the couple.

Alongside the picture of the ring, he wrote on Twitter: "Ahh! Congratulations to my brother... and sister in law to be on your engagement. I love you both so much. @joejonas @SophieT (sic)."