Sam Smith has revealed that he penned the new James Bond theme tune in less than half an hour.

The singer finally announced today (September 8) that he has recorded the song 'Writing's On The Wall' for upcoming spy film Spectre.

Speaking to BBC Radio 1's Nick Grimshaw after revealing the news, Smith said that it only took him a matter of minutes to write the tune after reading the film's script.

He said: "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."

'Writing's On The Wall' was co-written by Jimmy Napes, who helped form Smith's hit tune 'Stay With Me'.

Spectre will be released on October 26 as Daniel Craig once again stars as James Bond.

Fans will be able to buy the theme tune from September 25.

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Watch Sam Smith in action below: