Bradley was diagnosed with neuroblastoma in 2013, a terminal cancer which attacks the nervous system.
Although he was told he was in remission in December 2014 after several operations and a first bout of chemotherapy, the cancer returned.
Bradley later became a football sensation often acting as a Sunderland mascot, leading the team out for Premier Leaguegames.
He also led England out at Wembley for a World Cup qualifier against Lithuania.
He struck a special friendship with England striker Jermain Defoe who carries the kid with him out on most of his games.
His parents confirmed his death on Friday.
“He was our little superhero and out the biggest fight up but he was needed elsewhere. There are no words to describe how heartbroken we are.”