The best movies made expressive use of music. For example, Charli XCX's "Boom Clap" was perfectly used in The Fault in Our Stars, the film adaptation of John Green's novel of the same name. This raises an interesting question: did the book directly inspire the song? Charli XCX had something to say about that -- and how she reacted to the movie.

While "Boom Clap" appeared in The Fault in Our Stars, but it wasn't intended for that film initially. Charli XCX tried to sell the song to former Disney star Hilary Duff before singing it herself. Ultimately, the track appeared on the film's soundtrack.

During a 2014 interview with MTV News, the "I Love It" singer revealed that she had not finished The Fault in Our Stars. "I have it here!" Charli XCX laughed. "I've been carrying it around with me, and I've nearly finished. I saw the movie before I got the book, and the movie made me cry, it's amazing. It's going to affect a lot of people."

While Charli XCX had not finished Green's novel, she was happy to hear that "Boom Clap" was in the book's film adaptation. "I'm excited that people are going to hear my song and that it's part of a really good teen movie, because we haven't had one in a while," she said. "The Fault in Our Stars feels like The Notebook." The "Apple" singer revealed her favorite teen movies were The Craft and Charlie's Angels (though nobody else has ever called Charlie's Angels a teen movie).

Charli XCX discussed the meaning of "Boom Clap." "It's just about being epic-ly in love," she said. "Being totally immersed in passion and feeling really safe and really alone with that person. Although I always hear a tinge of sadness in it, that song has quite an acute feeling."

In 2013 and 2014, Charli XCX had three top 10 singles on the Billboard Hot 100: "I Love It," a collaboration with Icona Pop, "Fancy," a collaboration with Iggy Azalea, and "Boom Clap." "Boom Clap" was both the best of the bunch and Charli XCX's only solo hit from that era. While "I Love It" is a funny dance song and "Fancy" is a regrettable pop-rap hit, "Boom Clap" is a beautiful love song that sounds just as good today as it did in 2014.

"Boom Clap" reached No. 8 on the Billboard Hot 100, lasting on the chart for 25 weeks. The track was the centerpiece of the album Sucker. That album peaked at No. 28 on the Billboard 200 and lasted on the chart for eight weeks.

Sucker spawned three other singles: "Break the Rules," "Doing It," and "Famous." Only "Break the Rules" charted in the United States. It merely reached No. 91 on the Billboard Hot 100 and charted for three weeks. While Sucker wasn't the biggest hit of the year, it paved the way for the critical and commercial acclaim that she experienced with her album Brat.

While Charli XCX hadn't finished The Fault in Our Stars when she wrote "Boom Clap," she still penned a song that perfectly suited the movie.