Kelly Clarkson's "staying strong" but is "heartbroken" for her kids after ex Brandon Blackstock's death, a source tells PEOPLE. The singer and her late ex-husband share daughter River, 11, and son Remington,

She always wanted her kids to have the best relationship possible with their dad,” a source told People on Thursday.

Kelly Clarkson's ex husband and father of her two children, Brandon Blackstock, has died, and the family's loss makes their last Instagram posts even sadder.