ろう

probably, I suppose, right?

ɾ o̞ː → だ
auxiliary · informal Rare #28,687
probably, I suppose, right? An auxiliary attached to the plain form of a verb or to a noun or adjective with だ. It expresses a guess or seeks confirmation; it can sound conversational.
JA: 彼はもう帰ったろう。
EN: He’s probably already gone home.
Conjugation of だ

あの女の子を追いかけて階段を上って行ったろう

You chased that girl up the stairs, didn't you?

— M - Eine Stadt sucht einen Mörder (1931)

進二あの島は見たろう

You saw that island, didn't you, Shinji?

— High and Low (1963)

今はそうでもないが俺はこだわりの強いタイプではなかったろうか。

I’m not so much anymore, but wasn’t I once the type to be very particular about things?

彼は言わなかったろうな。

He probably wouldn't have said that.

— アトランティス 失われた帝国 (2001)

言ったろう

I told you, didn't I?

— Godzilla Minus One (2023)

お前の金だろう?

It's your money, isn't it?

なんてすばらしいコンサートだったろう。

What a wonderful concert it was!

Sounds similar to