I think this is the first time I've talked about it.
"初めて話したとおもう"
- I think this is the first time I've talked about it.
- This is probably the first time I've talked about it.
A：実は猫を７匹飼ってるんだ
B：え！？そうなの！知らなかった
A：多分初めて話したとおもう笑
A: I actually have 7 cats.
B: What?! Really?! I didn't know.
A: I think this is the first time I've talked about it lol
A：実は猫を７匹飼ってるんだ
B：え！？そうなの！知らなかった
A：多分初めて話したとおもう
A: Between you and me, I have seven cats at home.
B: Do you? I didn't know that.
A: I don't think I have told you before.
"I think it's the first time I've mentioned it"は、そのことに対して自然に言える英語表現です。"mentioned"は「話に出す、言及する」という意味で、伝えたい内容が初めて言及されたことを示しています。
例えばシンプルに：
A: I actually have seven cats.
B: Really!? I didn't know that.
A: I think it's the first time I've mentioned it.
アメリカ合衆国 
日本 
