Sam Smith is ''s****ing'' himself over the release of his Bond song.

The Grammy and BRIT Award winner will unveil his eagerly anticipated anthem 'The Writing's on the Wall' today (25.09.15) - which will serve as the main soundtrack for new movie 'SPECTRE' - and he admits the pressure to meet the high standard of previous Bond themes is ''quite intense''.

He said: ''I'm sh****ing myself. With this song I don't care about it charting and things like that. I just care about doing the legacy proud.

''The pressure to deliver a Bond song that stands against all the rest feels quite intense.''

The 23-year-old star's ''top secret'' Bond song has only been heard by a select few, including 'SPECTRE' director Sam Mendes, close friends and family, and of course, 007 star Daniel Craig.

Sam says filmmaker Mendes even had a hand in writing the lyrics to ensure the famous spy didn't come across too vulnerable.

He explained to The Sun newspaper: ''I feel like my music can be very vulnerable and I wanted to have a touch of that with Bond and have him sounding more vulnerable than normal.

''With Bond songs you get to be as dramatic as you want. I got to get away with unbelievable string and brass sections -- I got to be a drama queen.

''Sam had a say in some of the lyrics I was writing and made sure Bond didn't sound weak, that he still sounded powerful.''