Luke Bryan thanked fans for prayers after his niece Sadie Brett died on Tuesday (Feb. 21). The girl was battling an infection that affected her liver. She'd been battling heart issues as well.

Sadie Brett (known as Brett) is the daughter of Bo and Ellen Boyer, on Bryan's wife Caroline's side of the family. A representative for Bryan tells Taste of Country that the little girl was Caroline's brother's child. Very few details are available publicly, but a look at Ellen Boyer's Facebook page reveals the little girl had been dealing with internal issues for some time and treatments included dialysis. Several weeks ago she reported another infection, but since then the baby's health has been up and down. On Feb. 16 Boyer wrote that they'd had the best week of the year, but just three days later she was once again asking for prayers. A final Facebook update came on Sunday night. "Please flood the heavens with prayers. We will not give up on our tough, brave Brett," she wrote.

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News of the little girl's passing began to circulate on Tuesday with various tributes and word-hugs being directed toward the singer. His response came that afternoon:

The singer had been keeping fans updated on his app in recent months. Two months ago he shared that she was being treated at Vanderbilt, but mostly expressed hope and gratitude for the many prayers.

Bryan's family are no strangers to tragedy, but thus far it's come on his side of the family. The story of how he lost both his brother and sister in separate incidents has been told often. In December 2014 his late sister's husband also died, leaving him and Caroline as the providers for their son. Through it all he's maintained a positive outlook, only rarely revealing his emotions publicly.

See Country Stars Who've Lost Children