Boom Clap

"Boom Clap" was written during sessions for True Romance by Charli, Fredrik Berger, Patrik Berger and Stefan Gräslund. She offered it to Hilary Duff for her new album, and when Duff's management declined she used it for the soundtrack of The Fault in Our Stars. Duff later said she had no idea it had been offered to her and would have accepted. The song also appears on Sucker.

It peaked at number six in the UK and number eight on the Billboard Hot 100, and topped the Mainstream Top 40. In the US it has sold more than 3 million copies. It was her first top-ten hit as a solo artist after her features on "I Love It" and "Fancy". Spin put it at number 24 among the best songs of 2014 and Pitchfork at number 37. The video was filmed in Amsterdam and premiered on 2 June 2014.

She first performed it on a Fault in Our Stars live stream on 14 May 2014, then at the MTV Video Music Awards pre-show on 24 August 2014, and on Saturday Night Live. On 3 October 2015 she sang it at Taylor Swift's 1989 World Tour show in Toronto.