The loss of Clarkson's ex-husband Brandon Blackstock has left her "devastated" for daughter River, 11, and son Remington, 9.
Clarkson and her ex had a messy divorce, leading to a lengthy legal battle. Yet Clarkson, 43, never shared negative remarks with the kids about Blackstock, who died last week at age 48 after a three-year battle with cancer.
Those close to the inaugural American Idol winner said she kept Blackstock an active part of their lives after the split and didn't want her kids to have a relationship sadly similar to the one she has with her own dad.
"They are essentially estranged," an insider told Page Six about Clarkson's communication with her dad, Stephen.
"Kelly has had a very strained relationship with her own father her entire life," the source added. "When she and Brandon first got together, he had stressed to her how important it was that his relationship with his kids remained strong.
"Their bond wasn't going to end just because that marriage did."