Remember back in the day, about this time last year, when Taylor Swift's relationship with Calvin Harris was coming to a most dramatic end?
Oh, what a deliciously dramatic time that was.
Taylor had been dating Calvin for well over a year, and their relationship was quiet and private, but the breakup was anything but.
They split, she was spotted frenching Tom Hiddleston on a beach shortly after ... and things got nasty.
But more on that in a minute.
OK, now let's shift back one more year, to this time in 2015: Taylor was just about to release her music video for "Bad Blood," the song widely rumored to be about Katy Perry.
See, Katy and Taylor used to be friendly, but had a falling out after, according to Taylor, Katy "basically tried to sabotage an entire arena tour."
Katy had some backup dancers on a tour, and then later the same dancers toured with Taylor. In the middle of Taylor's tour, Katy's people asked the dancers to come on her new tour, and they did.
Is that enough to fuel a feud for the ages? It's hard to say.
But the point is that Taylor considers Katy a mortal enemy, she had her worst breakup yet with Calvin Harris, and now something truly delightful is happening.
Calvin is releasing a new album next month, and one of the tracks will feature Katy.
Oh, the shade of it all!
It's extra amazing because last summer, when things were getting extra messy with Taylor and Calvin, Calvin was the one who actually named Katy as Taylor's arch-enemy for the first time.
Remember, Taylor tried to take credit for writing his hit song "This Is What You Came For," and he wasn't having it.
"Hurtful to me at this point that her and her team would go so far out of their way to try to make ME look bad at this stage," he tweeted.
"I figure if you're happy in your new relationship ou should focus on that instead of trying to tear your ex bf down for something to do."
"I know you're off tour," he continued, "and you need someone new to try and bury like Katy ETC but I'm not that guy, sorry. I won't allow it."
"Please focus on the positive aspects of YOUR life because you've earned a great one."
Katy responded with a "told you so" Hillary Clinton gif, and she retweeted an old tweet of her own: "Time, the ultimate truth teller."
So for the two of them to come together now for a song, after all that went down ... it's going to be interesting, that's for sure.
And it seems like most people are Team Taylor on the matter.
"People are stupid if they think Calvin's collab with Katy is not out of his pettiness towards Taylor like c'mon," one person tweeted.
Another wrote "Katy Perry and Calvin Harris went from this mess to a collaboration for pettiness. The power of Taylor Swift and her savage ice queen ways."
And since "petty" seems to be the word of the day, one more Taylor fan wrote "THE POWER OF TAYLOR SWIFT Calvin and Katy collab is happening. I hope your two petty asses credit Taylor Swift for it!"
Whatever the reason for the collaboration and whatever comes from it, we are 100% here for it.
Calvin's album drops on June 30th -- see you then!