Kelly Clarkson’s top priority is her kids after her ex-husband Brandon Blackstock’s death. The “Since U Been Gone” singer, 43, has “been devastated” for her daughter, River, 11, and son Remington, 9, whom she shared with Blackstock, ever since their father was diagnosed with cancer over three years ago.

Kelly Clarkson has “been devastated” for her kids River, 11, and Remington, 9, as their dad Brandon Blackstock, who died on Thursday, Aug. 7 at age 48, faced cancer for three years privately, a source tells PEOPLE exclusively.

Clarkson, the "American Idol" star who shared two children with Blackstock, had just announced she was stepping away from concerts to support her family.