The Culture Club star was backed by a choir made up of cancer doctors and nurses from all over the U.K. and he told the TV event's host Davinia MCCall he was devastated by Bowie's death, revealing it was "like losing a family member".
"I think to a lot of people who grew up in the 70s he was like one of our relatives, he was part of us," the singer added. "It really hit everybody."
Bowie died in January (16), just two days after turning 69, following an 18-month battle with liver cancer.
Boy George also explained cancer has hit his family too, counting off the number of people he has lost to the disease: "My grandmother, my aunt two years ago, a close friend very recently. I know so many people who are fighting it. What's amazing is that people are really fighting now. There's a real spirit, there's a defiant spirit."
This year's U.K. Stand Up To Cancer event was dedicated to actress Caroline Aherne, who lost her battle with the disease in July (16), aged 52.
Steve Coogan paid tribute to his late pal during the telecast, stating, "She mercilessly took the p**s and she made me and a small gang of Manchester friends laugh until they cried. She was both ordinary and extraordinary. I never thought Caroline would become famous, she seemed too real, too genuine."