Zedd Collaborator Matthew Koma Rips Producer as 'Toxic,' 'Abusive' and Just 'the Worst'

This probably isn't the anniversary present Zedd was hoping for.

Matthew Koma, who collaborated with the DJ/producer on the mega-singles "Spectrum" and "Clarity," used the 7-year-anniversary of "Spectrum's" release to put Zedd on blast for his alleged behavior in the time since.

Koma -- who's currently engaged to Hilary Duff -- co-wrote both tracks, with his voice taking the lead in "Spectrum." After being asked by fans why the two didn't continue to work together after those hits, Koma posted a lengthy series of notes explaining their volatile relationship.

"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 to toxic and self serving that it occupied the space where any happiness could exist," he wrote.

Adding that it's not "that dramatic of a story," he boiled it down to: "Shitty people suck and when they're successful, people are afraid to blow the whistle."

As he kept writing, Koma claimed the "blows" began with little things, with Zedd allegedly taking credit for writing the songs. "I wrote every word and melody," said Koma. He also claimed Zedd prevented him from being paid for singing on "Spectrum" until years later and delayed the release of his own music.

The singer then alleged it was his idea to find a singer who "could really nail" the vocals in "Clarity." He added, "I wanted it to be great for him. He won a Grammy for it - I wasn't invited."

"More or less, I was just brushed under the rug while he took all the credit," he continued, "which felt 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 said his experiences weren't unique to just him.

"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," he wrote.

After applauding the many artists he's worked with who "treated me with mutual respect," he said "ego" and "success" are all too often a cause for disaster.

"But for those always wondering why there was never more music from the two of us, it wasn't really my choice," 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 toilers than ever experience that abusive dynamic again. Toxicity doesn't breed happiness. Alexa, play 'Happy Now.' Actually please don't."

Zedd has yet to respond on social media and his reps weren't immediately available for comment.

After his post went live, Duff also commented on Instagram, writing, "This is so important for people who love the music to know. Writers are taken advantage of, ignored, and mistreated. Proud of you for finally speaking up."

Bebe Rexha also commented, "The unfortunate dark side of the music business" -- and actor Christopher Mintz-Plasse added, "Hell yes. Get the word out man. Can't get treated that way."

Read Koma's note in full below: