You'd better to say "사실이다." or "진실이다." in formal situations or writing.

But it can be different according to situations.

If you tell me  exact situation, it can let you know ^^

Of course it is easy to get overwhelmed by the complexity of the language. So I guess the key is to take small steps at a time. After a little while you'll get used to the sentence structures and the different politeness levels~~

^^

thank you very much for the feedback. What if I were to put this sentence as a lyric in a song and the sentence "it is true" was something I was telling someone about life or love, it wont really matter to put it in a formal way, right?

I believe I've heard that the formality doesn't really matter when based in creating a poem/song because the artist may focus on how it sounds according to the beat or meaning in the song. therefore does it mean I could truly just used any translation?

Thank you very much!

However, If I were to use the sentence to write a song/poem would there be a specific type of way to say it?