Songfacts®:

• Alex & Sierra are 2013 X Factor winners Alex Kinsey and Sierra Deaton. "Little Do You Know" is their most popular song, resonating with couples who go through a stage where they question their relationship but emerge stronger.
  
  The song stars with Sierra singing about how she's scared and conflicted. Alex takes the next verse, letting her know that her feelings are valid, but he's fully committed and will give her whatever she needs. They come together in the end secure in knowing they'll love each other until the sun dies.
  
  Alex and Sierra were a real couple, which gave the song a lot of energy and honesty, but their love didn't outlast the sun. They broke up in 2016 and dissolved the duo a year later.
• Sierra Deaton wrote this song with three top songwriters: Ali Tamposi, Toby Gad and RuthAnne. Tamposi co-wrote Camilla Cabello's "Havana" and several songs for Miley Cyrus; Gad's hits include "Untouched" by The Veronicas and "If I Were a Boy" by Beyoncé; RuthAnne's CV includes Nial Horan's "Seeing Blind" and "Nice To Meet Ya."
  
  Most songs Alex & Sierra recorded were co-written by at least one of them. After their split, Sierra did a lot of writing for other artists, including the 5 Seconds of Summer track "Older," which she also sings on. Sierra and 5 Seconds of Summer frontman Luke Hemmings announced in 2024 that they had gotten married.
• "Little Do You Know" was Alex & Sierra's second single, following "Scarecrow." It was a late bloomer. The song didn't chart and didn't get much attention when it was released, but around 2020 it started finding fans, thanks largely to TikTok, where it became a popular soundtrack for videos. It's since gone well over a billion streams to become far and away the best known song in the Alex & Sierra catalog, with most of those streams coming years after the duo disbanded.
• The music video was shot in Los Angeles in an all-nighter so they could get the closing shot of the sun coming up, which brings it all together with the line "I love you till the sun dies." In the scene where Alex Kinsey is sleeping, he really did fall asleep - it was 2 a.m.!
  
  The director was Jay Martin, who also helmed the "Hey There Delilah video for the Plain White Ts.
• "Little Do You Know" got an update in 2024 when the song's co-writer Toby Gad recorded it with Keke Palmer and Aloe Blacc for his Piano Diaries album. "Kiki Palmer and I, we go way back," Gad told Songfacts. "I've worked with her when she was 12 years old, wonderful artist."