Skrillex and Diplo recently went to UK's Reading Festival for a performance as the super-duo Jack Ü. During the set, Skrillex and Diplo decided to live stream part of their set and tease their unreleased collaboration with the vocalist Florence Welch for the very first time. The song which was originally teased back in March got the final version as heard in the video below.
Listen to the rip of the song on YouTube before its removed. Still no mention of when the official song will be released.
Source: /r/Skrillex