But the Max Martin-assisted song is also - very clearly - Ellie's response to Ed Sheeran's Don't.
Don't, you may remember, was about Ed's relationship with Ellie, and how she (allegedly) left him for One Direction's Niall Horan, while they were all staying in the same hotel. It sounds like this.
On Ellie's song, On My Mind, she also she sings about being in someone's hotel room. He is making grand declarations of love - but she isn't keen. "You wanted my heart, but I just liked your tattoos," she sings.
And If the song really is about Ed, it seems that Ellie's feelings were hurt when he spilled his guts on Don't. "You mess with the truth," she accuses, "saying that I hurt you, but I still don't get it... You didn't love me. Not really."
But in the chorus, she gives a clue as to why it all rankled so much... "So why have I got you on my mind?" she asks. "I could have really liked you."
What a convoluted (but fascinating) tale. I look forward to hearing Niall's version of the story on One Direction's next album.
"It's been a long time coming. Love Me Like You Do... was never really meant to happen. I thought I was doing that for the film then it all kicked off. All of a sudden it was like 'she's back'. Now I'm really back. I'm back and it's just me."
Discussing On My Mind, she added:
"This was the first song I wrote with Max Martin. We met when we did Love Me Like You Do, and we got on really well. He's brilliant, he's hilarious.
"It's all very relaxed there. It's not like you go in and say, 'right, let's write a song'. It's more like we just chat about things for a day, and the next day we start thinking about writing some lyrics. The more I talk, the more ideas I come up with to write about."
You can hear the full interview (there's about 45 minutes of it) on the BBC iPlayer. Ellie first pops up at around 1h 45min into the show.