"The split is amicable and the pair continues to have nothing but the utmost respect for one another," Osbourne's rep told Us Weekly in a statement. "Kelly is looking forward to a new year full of fresh beginnings. No further comments will be provided by all parties and we request privacy, decorum and space from the press but don't expect it."
Osbourne, 29, met Mosshart at Kate Moss' 2011 wedding and went public as a couple later the same year.
The couple, last seen together at the amfAR Inspiration Gala on December 12, announced their engagement in July 2013.
"I've never felt this close to another human being, ever," Osbourne told HELLO! magazine at the time. "People say we're co-dependent but we just want to be together all the time."