The couple temporarily separated last November, and then quickly reconciled and got engaged in December.
The tattoo artist confirmed the breakup with the DJ and producer Deadmau5 via a message on Twitter.
“Cheating on your loved one is the most hurtful thing one could do. I hate to have to admit that this relationship is indeed over…Onwards and upwards,” she tweeted.
Responding to a fan’s tweet, “Don’t take him back no matter what. Ur worth more than that,” Kat answered simply, “Never.”
Soon after her tweets, Deadmau5 posted a message on his Facebook page.
“Kat and I split in November and I moved back home to Toronto. During this time, while we were broken up, I did have relations with another woman,” he wrote. “Following that, Kat and I reconciled and I acknowledged being intimate with another person while we were estranged.”
“We did move past those issues, and I proposed to Kat in mid-December. At the end of June, it was clear that the relationship was not working and we mutually ended the engagement. I was not, at any point, unfaithful to Kat during our time together.”
Kat Von D’s previous relationship with Jesse James ended after less than a year in September 2011.