Jonathan Cropper was the half-brother of Roy Cropper and the eldest son from his father's marriage to Margaret Cropper.
Due to his estrangement from St. John, Roy was unaware of the existence of his half-siblings until he visited Margaret at her home in Blackburn in May 2013 following his father's death. Margaret mentioned that Jonathan lived close by, while his younger brother Stephen and sister Isabelle lived in New Zealand and Cornwall respectively.