And to think we’d almost forgotten about this feud…

As recently as three years ago, singers Katy Perry and Taylor Swift were bosom buddies, appearing arm-in-arm at awards ceremonies, parties and fashion weeks.

But their relationship has in more recent times soured – and Taylor Swift's recent Bad Blood video is widely believed to be a dig at her former BFF.

Now Ms Perry appears to be on the war-path herself: she has legally and officially registered a song called 1984 with BMI, a major music publisher.

The significance? Her nemesis released the massively successful 1989 album last year to critical and commercial acclaim.

Coincidence… we think not.

The pair are believed to have met around 2009, and they shortly afterwards struck up a friendship.

In the preceding months, Taylor, 25, and Katy, 30, would regularly Tweet at each other, also posting cosy images together on social media. Ms Perry even made a guest appearance on stage at one of Tay-Tay's shows.

But by 2012 things had begun to turn sour. And then a year ago, the feud was pretty much confirmed when Taylor revealed the inspiration behind Bad Blood.

"For years, I was never sure if we were friends or not," she said in an interview with Rolling Stone. "She would come up to me at awards shows and say something and walk away, and I would think, 'Are we friends, or did she just give me the harshest insult of my life?'"

She added that in 2013, this person then "did something so horrible, I was like, 'Oh, we're just straight-up enemies'".

Ms Swift continued: "It had to do with business. She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me."

Meanwhile, in response Katy herself Tweeted a reference to the film, Mean Girls, and later unashamedly admitted it was directed at her one-time pal. And evidently she feels the battle isn't over just yet.

Sadly, there is as yet no indication as to when 1984 might be released.