のは初めてだ

it's the first time that

→ の

phrase Uncommon #15,778

it's the first time that Follows a verb or clause to say that something is happening or has happened for the first time. The ending can change, as in のは初めてではないです (it's not the first time).

JA: 一人で飛行機に乗るのは初めてだ。

EN: It's my first time flying alone.

キスしてもらったのは初めてだ

This is the first time I've ever been kissed.

— ほんとうのピノッキオ (2019)

ドアが閉まってたのは初めてだ

It was the first time I'd ever seen the door closed.

— ファイト・クラブ (1999)

彼のような人に平等に扱われるのは初めてだ

It's the first time I've ever been treated as an equal by someone like him.

— どん底作家の人生に幸あれ! (2019)

“ラジオで天皇の声が聞こえたのは初めてだ”

It was the first time I’d ever heard the Emperor’s voice on the radio.

— ラストエンペラー (1987)

こんなに雪が降ったのは初めてだよ。

I've never seen this much snow before.

あんなことを人に言われたのは初めてだ。

That's the first time anyone's ever said something like that to me.

こんなに具合が悪いのは初めてだよ。

I've never felt this sick before.

雪がこんなに積もったのは初めてだ。

I've never seen this much snow accumulate before.