One Direction's new track 'Best Song Ever' has leaked.

The teen heart-throbs have been teasing fans with images from the upcoming video for the song - due out on Monday (22.07.13) - but they can now hear it in its entirety in a lyric video posted online.

The song will feature in the band's 3D movie 'This Is Us', and is also expected to be act as the first single from the boy band's eventual third album.

Despite the song being due out next week and the film being released on August 30, fans will have to wait until next year for a follow-up to the band's last album 'Take Me Home'.

The 'Little Things' hitmakers - Zayn Malik, Harry Styles, Niall Horan, Liam Payne and Louis Tomlinson - are becoming more involved with the writing of their new record, and Snow Patrol singer Gary Lightbody recently shed some light on his writing sessions with Harry Styles.

He previously said: ''We wrote with Harry. It was a lot of fun. He's a real dude actually. We've no idea if those songs will make it yet, though.

''It's a long process. It's great to work with other people - it's good to flex the muscle.''