可以说 顺便说一下 ，或者直接用 对了

歐! 對了Ōu! Duìle, ......blah blah blah

I have to say it is not unrelated to the prebious or the present topic. It is related indeed most of time. The things after BTW come to your mind is a result of the previous or the present topic.

在句子中做插入语。翻译为‘顺便说一下，顺便问一句，另外，对了，喔......等等。表示在说某一件事情的时候，突然想起另一件事。 By the way, what happened to the money? 顺便问一句，那笔钱后来怎么样了？ By the way,how is your work going recently? 对了，最近工作怎么样？

you can say..."對了順便跟你說一下" by the way, you answer pretty quickly!! 對了(順便跟你說一下)，你回答得非常快!