The Scottish music producer and DJ revealed the list all the people he's collaborated with on the record and Katy Perry is on it.
You know what they say, the enemy my enemy is my friend, and it looks like Calvin and Katy are pretty friendly.
His relationship with Taylor came to an acrimonious end in 2016 after a year together, before she moved on to Tom Hiddleston pastures new.
That romance was obviously one for the ages...
So it's really no surprise that Calvin wanted to work with his ex's music industry nemesis to really rub the salt in the wound.
Harris is known for holding a grudge - who can forget that time he stopped ex-girlfriend Rita Ora from performing the songs he wrote for her after their split?
Rita is allowed to perform them now as the pair have reportedly put their differences aside, but with this Katy Perry collaboration it may be a while before Calvin and Taylor are on good terms again.
Also collaborating with Calvin on the new album are Frank Ocean, Travis Scott, Kehlani, Future, Pharrell Williams, Big Sean, John Legend, Khalid, Migos, Schoolboy Q, Ariana Grande, Young Thug, D.R.A.M., Nicki Minaj, Lil Yachty, Jessie Reyez, PARTYNEXTDOOR, and Snoop Dogg
Katy is bringing out her fourth album soon, having recently shared an album track called Bon Appétit featuring Migos.
It's believed the album is called Witness and her track with Calvin may well appear on it.