By Mark Dagostino
April 21, 2008 12:00 PM

The day after he was rushed to a hospital for high blood pressure and heart palpitations, American Idol’s David Cook, 25, was back with his trademark smile. “The whole thing kind of got blown out of proportion,” the affable rocker told Ryan Seacrest on the show April 2. “I’m not going anywhere.”

What Cook didn’t reveal was that he’s coping with more than the typical Idol pressures: His half brother, Adam Cook, 36, is undergoing treatment for cancer. Says Kenneth Cohen, Adam’s father-in-law: “David and Adam are very close. David was just down [in Indiana, where Adam lives] two weeks ago visiting him.”

Adam, an attorney who is married with two children, was diagnosed with brain cancer in 1998, several sources say. In remission until 2006, the cancer has now spread, and Adam is undergoing chemotherapy. David and Adam were both unavailable for comment. “David doesn’t want American Idol to overshadow this very important fight,” says Susan Cooper, David’s former theater teacher in his native Blue Springs, Mo.

Last year’s Idol winner, Jordin Sparks, understands the strain: She lost a friend, her uncle and her grandmother during the contest last year. “You have to go out there and put this smile on your face. It’s exhausting, and it gets to you,” Sparks says. “David is definitely in my prayers.”