Los Angeles, Sep 9 (IANS): Singer Sam Smith, 23, says writing the theme song for new James Bond adventure "Spectre" was a "top secret mission of my own", and that he eventually penned it in 20 minutes.

He was thrilled to be asked to write "Writing's On The Wall", the official song for "Spectre", the 24th installment in the 007 franchise, reports femalefirst.co.uk.

During a radio show on BBC Radio 1, Smith said: "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."

Smith co-wrote the track with Grammy Award winner Jimmy Napes and is the first British male solo artist to record the Bond theme since Tom Jones' "Thunderball" in 1965.

"Writing's On The Wall" will be released on September 25, while "Spectre" will release in Britain on October 26 and in the US on November 6. In India, it will release on November 20.