その事を

that matter

→ 其の
phrase Rare #21,449
that matter Refers to a matter or thing already mentioned or understood from context; を marks it as the object of the verb.
JA: その事をもう一度説明してください。
EN: Please explain that matter one more time.

その事を両親に言ってはいけない

You mustn't tell your parents about that.

明日彼とその事を話し合うことになっている

I’m going to discuss it with him tomorrow.

その事を考えただけで楽しくなる

Just thinking about it makes me happy.

一体どうしてその事を知っていた

How on earth did you know about that?

彼ら自身その事を知らなかった

They themselves didn't know about it.

その事を僕に隠さないでください

Please don't hide that from me.

ジャックその事を深く後悔しているようだ

Jack seems to deeply regret it.

その事を聞いたのはジョンしかいない

John is the only one who heard about it.