Matthew Koma has blasted Zedd for his "toxic and self-serving" actions.
Matthew Koma and Hilary Duff
The 32-year-old songwriter - who is engaged to Hilary Duff - has launched a scathing attack on the EDM producer for taking the credit for all of the lyrics on their hit songs 'Clarity' and 'Spectrum' released in 2012.
In lengthy iPhone notes shared on his Twitter page, Koma wrote: "In response to years of: 'What happened with you & Zedd.' I want to finally be transparent about this.
"it's a really sad truth because I'm extremely proud of the work he and I did together. Unfortunately my good feelings toward those songs have all but disappeared as they were experienced alongside someone so toxic and self serving that it occupied the space where any happiness could exist.
"It's not that dramatic of a story and it comes down to something simple.
"S***** people suck and when they're successful, people are afraid to blow the whistle ... (sic)"
Koma also claimed the German-Russian multi-instrumentalist - whose real name is Anton Zaslavski - told him he didn't want his name to feature on 2014 song 'Find You' and that he was the one who suggested the singer Foxes provide vocals on mega-hit 'Clarity' , but he wasn't acknowledged for his efforts.
He fumed: "He won a Grammy for it - I wasn't invited.
"There was a documentary about 'the making of Zedd' and I was the only collaborator not invited to the premiere or asked to be interviewed for the movie."
He continued: "More or less, I was just brushed under the rug while he took all the credit.
"Confusing because the millions of people who connected to 'Clarity' and those other songs, seemed to connect to the lyrics/emotion/melodies I had written. But he deemed his Kick Drum sound the driving force and left me out of all shared credit."
Koma - who has worked on songs for the likes of Kelly Clarkson, Shania Twain and 5 Seconds of Summer - also accused Zedd of doing the same thing to other people he's worked with in the industry.
He wrote: "For years I thought maybe it was me, but over time, I'd run into other people who worked with him, other writers/singers/producers/DJs/people on his own team, and the sentiment was shared. He's the worst."
Whilst he admitted that he would rather "clean toilets" than work with him again.
He added: "Now, he has plenty of people to write his songs and produce his tracks and help him continue on his trajectory.
"But I rather work at Starbucks and clean the toilets than ever experience that abusive dynamic again. Toxicity doesn't breed happiness."
Zedd is yet to respond to Koma's outburst.
Tagged in Hilary Duff Foxes Matthew Koma