Billie Eilish at the 2019 LACMA Art and Film Gala in Los Angeles. Picture: AP

Billie Eilish flew in to London in secret to record the new James Bond theme tune, it has been revealed.

The 'bad guy' hitmaker has been announced as the youngest person ever to write and record the theme song for the iconic movie, with Billie and her older brother Finneas O'Connell's track being used on the upcoming instalment "No Time To Die".

And it has now been revealed Billie came over to the UK just before Christmas to write and record the song in secret, The Sun newspaper's Bizarre column reports.

Meanwhile, Billie recently confessed she is "still in shock" that she was chosen to write the new James Bond film theme song, ahead of the film's release on April 3, 2020.

She said: "It feels crazy to be a part of this in every way. To be able to score the theme song to a film that is part of such a legendary series is a huge honour. James Bond is the coolest film franchise ever to exist. I'm still in shock. Writing the theme song for a Bond film is something we've been dreaming about doing our entire lives. There is no more iconic pairing of music and cinema than the likes of 'Goldfinger' and 'Live And Let Die'. We feel so so lucky to play a small role in such a legendary franchise, long live 007."

Whilst producers Michael G Wilson and Barbara Broccoli added: "We are excited to announce that Billie and Finneas have written an incredibly powerful and moving song for 'No Time To Die', which has been impeccably crafted to work within the emotional story of the film."

The news was announced on the official James Bond Twitter account.

A statement posted on Twitter read: "The #NoTimeToDie title song will be performed by @billieeilish. Billie has written the song with her brother @finneas and is the youngest artist in history to write and record a James Bond theme song. (sic)"