1. 顺便谈及;顺便提一下
    You use incidentally to introduce a point which is not directly relevant to what you are saying, often a question or extra information that you have just thought of.

    e.g. 'I didn't ask you to come. Incidentally, why have you come?'
           “我没有叫你来。顺便问一下,你为什么过来?”
    e.g. The tower, incidentally, dates from the twelfth century.
           那座塔,顺便提一下,可以追溯到 12 世纪。

2. 附带地;伴随地
    If something occurs only incidentally, it is less important than another thing or is not a major part of it.

incidentally

    e.g. The letter mentioned my great-aunt and uncle only incidentally.
           信中仅附带提到了我的姑奶奶和叔叔。