初耳だ

that's the first I've heard of it

→ 初耳
phrase Uncommon #17,716
that's the first I've heard of it Used when something is new information to the speaker. 初耳です is the polite form; the ending can also change to express surprise or skepticism, such as 初耳だぞ or 初耳だわ.
JA: その計画については初耳だ。
EN: That's the first I've heard of that plan.

初耳だ

That's the first I've heard of it.

— フィールド・オブ・ドリームス (1989)

初耳だ

That's the first I've heard of it?

— キャッチ・ミー・イフ・ユー・キャン (2002)

これは初耳だ

This is the first I've heard of it.

そんな難しい言葉は初耳だ

I've never heard such a difficult word before.

— イル・ポスティーノ (1994)

この言葉は初耳だ

That’s the first time I’ve heard that term.

初耳だ

That's the first I've heard of it.

初耳だ

That's the first I've heard of it.

— フィールド・オブ・ドリームス (1989)

それは初耳だ

That's the first I've heard of it.