(という)のは事実だ
Usage
S(という)のは事実だ is used when the speaker wants to claim that something is true or is a fact, or when he/she admits that something is true or is a fact. The presence of という does not change the meaning. It is {true/a fact} that -
Examples
この教科書を使うようになって、学生達の日本語がどんどん上達したというのは事実だ。
It is a fact that the students' Japanese has improved significantly since they started using this textbook.
東京は物価が高いことだけでなく、土地も狭いので、暮らしにくいというのは事実だ。
It is a fact that living in Tokyo is difficult, not only because of the high cost of living but also due to the limited space.