I'm looking for a word that I can use to start a sentence which would indicate that the rest of the sentence gives information which isn't really important.
For example:
If you want to know, I saw that same black car yesterday on the parking lot.
The only word I could think of is the word Informatively but it doesn't really have the same tone like in the example.
I can think of a few ways to start the sentence,
Interestingly enough can be used to "introduce a piece of information that the speaker finds surprising and interesting" (Cambridge Dictionary).
Interestingly enough, I saw that same black car yesterday on the parking lot.
Believe it or not means "you may choose to accept something as true or not; it may seem amazing but it's true" (The Free Dictionary).
Believe it or not, I saw that same black car yesterday on the parking lot.
Merriam Webster defines incidentally as "by way of interjection or digression : by the way".
Incidentally, I saw that same black car yesterday on the parking lot.
By the way, I saw that same black car yesterday on the parking lot.
