The 54-year-old from Melbourne pleaded guilty to manslaughter on March. 13.
He was due to stand trial the following day at the Victorian Supreme Court.
Borce Ristevski had been accused of killing Karen, who went missing from the couple's Avondale Height's home in Melbourne's northwest in June 2016.
Karen's body was found eight months after she went missing, in bushlands in the Mount Macedon Regional Park.
Prior to his admission, Borce's daughter Sarah was revealed as a shock prosecution witness in the case against him.
He had long denied any involvement in Karen's death - claiming his wife had gone on a walk and never returned.