peter has just arrived ,and i didn't know he was coming until last night

问题描述:

peter has just arrived ,and i didn't know he was coming until last night
为什么用was coming ,用had come 不行吗

不行,后面有last (这是过去式),用was coming是过去进行时,表过去正在发生的事情had come 过去完成时,不也是过去已经发生么?我不知道他昨晚已经来了??