David Cook [ tickets ], who served yesterday (5/3) as an Honorary Chairperson of Washington, DC's, 12th Annual Race for Hope, announced to the event's 9,000 participants that his older brother had died the previous day from a brain tumor, according to a People report. Adam Cook, 37, had been battling cancer for more than a decade.

After the season seven "American Idol" winner shared his family news, he reportedly told the crowd that he couldn't imagine being anywhere else but at the charity race, which benefited the National Brain Tumor Society and Accelerate Brain Cancer Cure.

"When I was competing to win 'American Idol,' I came to understand the power of grassroots support," Cook said in a statement on his website. "I strongly believe this same enthusiasm is the key to unlocking a cure for brain cancer. ... As you know, this cause is very close to my heart."

Cook's team raised more than $98,000 for the cause; in total, the event raised approximately $2 million. After the race, Cook spent the afternoon hugging cancer survivors, signing autographs and taking pictures, event organizers reported.

Adam Cook, who was undergoing chemotherapy for his second diagnosis of brain cancer during his sibling's run on "Idol," had an opportunity in April 2008 to sit in the front row and watch his baby bro perform. The younger Cook often paid subtle tribute to his brother during his "Idol" performances by sporting the initials "AC" in various places, including on his guitar and jacket.

Adam Cook, a former lawyer in Terre Haute, IN, is survived by his wife, Kendra Cook, and two children ages 6 and 7.