You use incidentally to introduce a point that is not directly relevant to what you are saying, often a question or extra information that you have just thought of. 顺便说及地
adverb [方式副词]顺便说一句;偶然地;附带地,伴随地
"I didn't ask you to come. Incidentally, why have you come?" “ 我没有叫你来。顺便问一下,你为什么来呢?”