As Kelly Clarkson has been navigating the unimaginable death of her ex-husband, Brandon Blackstock, , her children have always "come first." "It has been draining, exhausting, emotional [and] devastating," a source exclusively tells Us Weekly of Blackstock's diagnosis and untimely passing. News broke on Thursday, August 7, that Blackstock died at the age of 48, after a private three-year battle with cancer.