British pop star Sam Smith has been confirmed as the artist behind the theme song for new James Bond movie Spectre, just weeks after the singer declared he was "definitely" not involved in the project.

The Stay With Me hitmaker had been a favourite for the coveted job, but in July (15) he denied his involvement, declaring, "It's definitely not me" and suggesting singer Ellie Goulding was recording the track.

However, he dropped a big hint on Monday (07Sep15) by sharing an image on Instagram.com showing him wearing a ring emblazoned with the Spectre octopus logo, and Sony Pictures Entertainment executives have now confirmed the news.

Smith has co-written the track, titled Writing's On The Wall, with his regular collaborator Jimmy Napes, and it will be released on 25 September (15), ahead of the U.K. cinema release of Spectre on 26 October (15) and in the U.S. on 6 November (15).

Smith says,"This is one of the highlights of my career. I am honoured to finally announce that I will be singing the next Bond theme song. I am so excited to be a part of this iconic British legacy and join an incredible line up of some of my biggest musical inspirations. I hope you all enjoy the song as much as I enjoyed making it."

The singer tells BBC Radio 1 he recorded the track in January (15) and has been struggling to keep the news quiet, saying, "I'm so relieved to actually talk about this, this has been a top secret mission of my own.

"I got called into the office with (producer) Barbara Broccoli and (director) Sam Mendes and they gave me the script, I read the script... They said 'have a go at the song'... It's the quickest I've ever written a song - it took 20 minutes... and they loved it!... I love the song so much."

The last James Bond theme, Skyfall, was a huge hit for fellow British star Adele, winning her an Oscar, a Golden Globe and a BRIT Award.