Brandon Blackstock, the talent manager and former husband of Kelly Clarkson, died of melanoma, a form of skin cancer, on Aug. 7. The Silver Bow County Coroner Dan Hollis tells PEOPLE Blackstock "passed away peacefully at his home in Butte,

According to the official death certificate obtained by People Thursday, seizures were listed as “significant conditions contributing to death but not resulting in the underlying cause.” Kelly Clarkson’s ex-husband’s official cause of death was listed as malignant melanoma.