his friend and fellow author (was were) cool to the idea.要选W

his friend and fellow author (was were) cool to the idea.要选WAS吗?为什么?
看到之前一个回答正确答案是was.
有点不理解,为什么 His friend and fellow author 是指一个人?
and fellow +职业 是一个固定搭配用法吗?
还是有点不明白这个author authour好像是作为后置定语一样修饰前面的friend and fellow么？
his friend and fellow 这个我还能理解是同一个人，但是后面再来一个author就有点混乱了。(脸红)