The telling lyrics: "She's an angel / My only angel."
Who it is supposed to be about: Kendall Jenner
Why? Some people think this song could be about Jenner, whom Styles is friends with and had somewhat of a romantic connection with a few years ago. The basis for this is really just that it's referencing an angel, and Jenner used to be a Victoria's Secret model. Beyond this clue, there isn't much tying this theory together, so take it with a grain of salt.