Speaking of their fairytale romance, Mosshart explained how he proposed to Osbourne after finding out she was "the one" early in their relationship.
"We were on a balcony that overlooks the ocean. It was just beautiful. She said yes! And then she smiled for the rest of the night!" he said adding, "I knew she was 'the one' pretty early on."
As for how she feels, the "Fashion Police" host told Hello! she's never felt this close to anyone before.
"People say we're co-dependent but we just want to be together all the time," she explained.
The 28-year-old fashion designer recounted that she met Mosshart at the 2011 wedding of Kate Moss and Jamie Hince and that he made the biggest sacrifice anyone has ever made for her by moving from New York to Los Angeles to be with her.
"Long-distance relationships often don't work out. We'd dated for a year and knew we wanted to be together. Matthew has broken down every one of my walls. There's nothing I wouldn't do in front of him," Osbourn said.
As for the engagement ring, Osbourne confessed she designed it herself.
"I designed it to look like an earring that my father wore," she said. "I used to hold my finger up to his ear when I was little and say: 'I want a ring like that'. Now I have one!"