Ed Sheeran wrote a James Bond theme three years ago ''just in case''.

The 'Castle on the Hill' hitmaker has never been approached to write a song for one of the iconic movies, but if bosses of the spy saga do ever knock at his door for help on the soundtrack, he's all ready to go.

Speaking on Ireland's 'The Late Late Show', he said: ''With Bond, I've had a theme tune written for about three years, just in case!''

And the 26-year-old singer admitted his collaboration with Eminem, 'River', was also something he had had ready for some time.

He said: ''I just recently did a song with one of my all time heroes, Eminem and when we did the song together I had already had this song. It's the same with Bond. If ever I am called, I will be like, 'Here you go.' ''

While Ed reassured fans his Bond theme is ''good'', he didn't want to give away any details about the song, including the title.

He said: ''I'm not going to say 'cause someone might steal it.''

Meanwhile, the 'Galway Girl' star recently admitted he would like to work more with Eminem in the future.

He said: ''I think I'd do two different songs with him and choose one of them. One of them would be like an introspective story telling thing like 'Stan' and one of them would be like - you know when he used to joke rap ... like in the shower this morning, I was doing 'I murder a rhyme, one word at a time/You never heard of a mind as perverted as mine.'''