LOS ANGELES (AP) -- Adam Cook, the eldest brother of "American Idol" winner David Cook, has died from brain cancer. He was 37.

David Cook announced the Saturday death at the 12th annual Race for Hope 5K in Washington, D.C., where he was serving as grand marshal. The singer says the cause of death was a brain tumor.

Adam Cook was a lawyer and married father of three from Terre Haute, Ind., who battled cancer for more than a decade. He famously cheered for his singing sibling in the audience of the popular Fox signing competition's seventh season finale in 2008.

Adam is the eldest of Cook's brothers. A younger sibling, Andrew, also tried out for the show but didn't make it to Hollywood.

The death was first reported by People.com.