Julian Bunetta & John Ryan
Lyrically, the song describes a person who appears to be famous, and who helps the narrator understand themselves better. The narrator sees themselves as a saviour for Diana. The other songwriters involved have confirmed the track is about a specific person, but would not reveal who she is.
Diana was originally leaked online on September 21, 2013.
The song debuted at number two on the Irish Singles Chart on 19 November 2013, the day after it was released.
In an interview with MTV News, when Julian Bunetta was asked if the song was named after someone called "Diana", he replied "Can't tell! It's definitely about somebody, maybe one day somebody will tell. But we can't tell. I think that the lyric probably pertains to what a lot of the fans are going through and feel... People feel like they're alone and that's what their escape is, Twitter and [finding] people that also relate to them, and everyone finding each other from different parts of the world that are going through the same things." He went on to say, "[I think] it was a kind of a pretty accurate depiction of the loneliness someone can feel in such a huge world and someone saying 'Hey, I feel you. I know you're there. I notice you; it's OK. You're not alone'."
Tomlinson told Perez Hilton's Danielle Sacco for Perez TV that, "We [were] actually working with a few different names for the chorus, and the top name originally was 'Joanna', which is actually quite close to my mum's name, and it felt a little weird so we changed it to Diana."
The day after its release, the song debuted at number two on the Irish Singles Chart, where it was one of three One Direction songs from Midnight Memories in the top 10, along with the album's title track "Midnight Memories" (number three) and "Story of My Life" (number six). "Diana" debuted on the Billboard Hot 100 at number 11 on 7 December and dropped off the chart the following week.