“All My Love” by Major Lazer featuring Ariana Grande is a electropop track written by Lorde, Grande, and MØ for the Hunger Games: Mockingjay – Part 1 soundtrack, which was also curated by Lorde.

The song is the fifth track off the album, and it was initially not revealed with the rest of the tracklisting on October 21st, however Lorde said this was not meant to be any sort of surprise, but simply because the track was unfinished.

https://twitter.com/lordemusic/status/524625567539150848

And eventually the song was finally announced on November 3rd:

https://twitter.com/lordemusic/status/529422037039591425