与come about 有关

题目

与come about 有关
how did it come about that such an unexpected event had happened?
这个句子怎么理解啊.翻译成什么,句子中的it应该是指代后面的THAT从句,

答案

come about 和 happen 有点重复
出这样一件意外事件是怎么发生的?