Delta Goodrem and boyfriend Matthew Copley announce engagement

Australia's sweetheart Delta Goodrem has announced her engagement to long-time boyfriend Matthew Copley in a sunset Instagram post from Malta.

"My best friend asked me to marry him," Ms Goodrem wrote, showing a massive diamond glittering on her ring finger with a view over a Malta harbour at sunset in the background.

White rose petals are scattered on the grass while a trio of violinists play.

Congratulations rolled in for the famous couple with a number of high profile figures joining Sophie Monk, Sonia Kruger and Lisa Wilkinson in well wishes.

"Now THAT's something to sing about," The Morning Show co-host Kylie Gillies commented.

"A Love time of happiness to you together," blogger and columnist Perez Hilton said.

The couple "met through music" and now tour the world together with Mr Copley playing guitar beside Ms Goodrem.

"It's incredible to be on stage with him because he's so talented. We really are a team. He's my best friend, he's kind and just a beautiful human being," she told Australian Women's Weekly in February.

"I'm very lucky. It's all very natural and I think that comes from a beautiful respect and love. I feel so grateful," she said.

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"I learnt quite young that I enjoy keeping part of that private. I've always been so understanding that I've lived in the public eye since I was a teenager but also I think it's nice to keep some things to yourself."

The couple have been tight-lipped about their relationship in interviews but post regular updates about their international touring adventures on social media.