Neither Dumbledore nor Grindelwald ever seems to have referred to this brief boyhood friendship in later life. However, there can be no doubt that Dumbledore delayed, for some five years of turmoil, fatalities, and disappearances, his attack upon Gellert Grindelwald. Was it lingering affection for the man or fear of exposure as his once best friend that caused Dumbledore to hesitate? Was it only reluctantly that Dumbledore set out to capture the man he was once so delighted he had met?
Extrat of The Life and Lies of Albus Dumbledore